Hollow World

aka: Hollow Earth

Old man: Years ago, I climbed the mountains, even though it was forbidden.
Kirk: Why is it forbidden?
Old man: I am not sure, [writhes and gasps in pain from a control device] but things are not as they teach us. For the world is hollow and I have touched the sky.

— Star Trek: The Original Series, "For the World Is Hollow and I Have Touched the Sky"

So, mainstream scientists today believe that the Earth under our feet has a lot of molten rock and metal filling it and have gathered a lot of pretty solid evidence for it. The only complication is that we've never been able to send a human down more than several miles to actually study it up close, largely because No One Could Survive That! Which is why since times that are Older Than Radio, early scientists, writers and more than a few crackpots have believed that there just might be something... or indeed, someone (say, Ultra Terrestrials)... down there, possibly powered by a suitably sized sun in the center.

The most known early example is Jules Verne's Journey to the Center of the Earth, although he likely drew from theories of his time. When science started to switch over to the modern view of Earth's composition the idea of the hollow earth became a Discredited Trope, but later generations of Speculative Fiction writers took up the concept and revitalized it, making it a staple of pulpy Two-Fisted Tales. Sci-Fi works bring us hollow world concepts such as the Dyson Sphere, which is a Hollow World taken to a solar system scale, and other variations of artificially constructed worlds.

Note that its usual configuration, with people walking about on the inner surface, wouldn't work; a hollow sphere has no net gravitational pull on any object inside it. Although some theorists, such as John Symmes, claim that this actually could work due to the centrifugal force caused by the planet's rotation. However, not only would this only work at the equator, it would still have to be very low, otherwise the planet itself would break apart.^note The centrifugal acceleration at Earth's equator is only 0.003g.

A related belief is that of "Concave Hollow Earth": that Earth is actually a hollow bubble inside an infinite mass of rock.

A sub-trope of World Shapes and, in more modern works, an example of All Theories Are True. Compare Beneath the Earth, Dyson Sphere, Planetary Core Manipulation. When the inhabitants don't know they're in a hollow world, it may become a City in a Bottle or a Lost World.

May contain Living Dinosaurs and/or Lizard Folk, The Morlocks, Fungus Humongous, the occasional Underground City, and at least one Crystal Landscape of unspeakable beauty.

Not to be confused with Hollow Earth the series.

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Examples

Anime and Manga

• The setting for most of Children Who Chase Lost Voices is Agartha, a massive underground world with a completely open sky. Any physical or geological impossibilities with this can seemingly be explained by the fact that God lives here.
• Doraemon
  • One comic issue centers around Nobita and Doraemon's discovery of a barren, hollow realm in the center of the Earth thanks to a gadget which warps any myth into reality in the eyes of its users. As you would expect from an adventurous kid and his multipurpose robot, the duo proceed to populate the space with life, including little clay people that rapidly form a fairly advanced civilization and eventually venerate the duo like gods.
  • Doraemon Nobitas Diary Of The Creation Of The World have Nobita creating a brand new world of his own using a Universe Creation Kit, but after realizing his world doesn't have mammals in it, only bugs, asks for Doraemon to speed up its evolution process. This leads to the creation of humans' ancestors, with bugs on the other hand being forced underground and creating their own civilization, a Hollow underground city populated by sentient, human-sized insects.
  • Doraemon: Nobita's New Dinosaur have an underground dinosaur sanctuary accessible through a cavern entrance, leading to a lost world populated by multiple different types of dinosaurs, including the last pockets of Nobisauruses the gang have spent the entire film searching for. This hidden sanctuary is eventually revealed as the result of a Chekhov's Gun from earlier - when Doraemon and friends accidentally arrived in the Jurassic period instead of the Cretaceous era, and Nobita lose the Breeding Diorama gadget along the way, turns out the gadget continues expanding on it's own and when they reach the correct time, said gadget already became a hidden world of various dinosaurs.
• Endride is set in Endora, a fantasy kingdom inside a hollow Earth. There is a large green crystal floating in the center that serves as their sun. And somehow there is an open green sky there.
• This is used in Maoyu. The "no gravitational pull" aspect is got around by having the sun be a repulsing force instead, pushing things away from it toward the ground.
• This is a main plot point in Spider Riders. Hunter finds the Inner-World in the very first episode.
• Dr. Suzuki in Transformers: Cybertron believes the world is hollow, with a hole at the North Pole leading to the inside. She's wrong, but there is a big massive cavern full of ancient Decepticons.
• The Fushigiboshi in Twin Princess of Wonder Planet, which gives it its name (which translates to "Wonder Planet").
• Mentioned in Ayakashi Triangle: Lu does not believe in the supernatural (which is real in this setting), but she does believe UFOs must somehow be connected to the hollow Earth city of Aruzaru^*A specifically-Japanese version of hollow Earth theory that seems to be a corruption of "Agartha"..

Comic Books

• Atomic Robo makes it very clear that the Earth is not hollow, because that would be scientifically impossible. However, there is an extensive, undetectable planet-wide cave network populated by an alien silicon-based ecosystem, created when debris from Theia was captured by Earth's gravity and sank into the crust billions of years ago. ^note An immortal magma worm was involved at some point. We don't really know how.
• In the miniseries Batman Odyssey, Batman travels Beneath the Earth and finds it hollow and filled with dinosaurs, trolls, wizards, monsters, and so forth. Neal Adams is on board with this idea.
• There's a B.P.R.D. story called "Hollow Earth". It features mutant cavemen and what looks like Nazi submarines. However, it's not quite a traditional version — it's more like there is a network of subterranean caves in various places around the world where said mutant cavemen (really former servitors of the ancient Hyperboreans) live, and most of the world seems to be largely as we know it aside from that. Agartha and similar legends from Theosophy and the Thule Society occasionally crop up in the broader Hellboy universe but the truth is generally rather off from what the Theosophists thought.
  • The spinoff comic Witchfinder has a malevolent spirit explicitly exploiting a group's beliefs in the Hollow Earth to feed off their collective life forces (and then their blood).
  • The hollow Earth caves turn out to be more important as the different Hellboy series progress. In the end they turn out to be the place humanity was destined to inhabit when the surface of the planet is destroyed.
  • The story Frankenstein Underground has Frankenstein's Monster getting stranded in the Hollow Earth, where he encounters the ruins of an attempt to colonize it by a group of Theosophist-style mystics, who were preparing for the apocalyptic event mentioned above. Naturally, the place is crawling with really cool monsters. He ends up deciding to stay down there, where he can finally be left alone and be at peace with nature.
• The Warlord: Skartaris was originally inside a Hollow Earth. A later Retcon changed it into an alternate dimension that was accessed through gates at the Earth's poles.
• Another DCU example: Steve Conrad, a Golden Age adventurer, explored a Lost World called Mikishawm inside the Earth.
• In the Marvel Universe, Saturn's moon Titan is this: barren on the outside, fully inhabited on the inside.
• In Society of Super-Heroes: Conquerors of the Counter-World #1, Immortal Man mentions in passing that he just walked back from inside the Earth.
• Super Dinosaur: The Earth is hollow and houses a smaller one: Inner-Earth, which is inhabited by dinosaurs. And the Reptiloids.
• In one issue of the Gold Key Underdog comic book of the 1970s, Underdog met many strange creatures, including a rock 'n' roll band, as he followed Simon Barsinister's drilling machine through the earth.
• Valérian: The inhabitants of the "starless country" live inside a hollow planet. The core is their sun. And yes, somewhere a physicist is crying.
• Wonder Woman:
  • Queen Atomia's Atom/Subatomic World looks like a sphere but every action there takes place inside and "underground".
  • Wonder Woman (1942): Queen Clea's Venturia and Queen Eeras' Aurania are both said to be Atlantean outposts but rather than underwater in their first appearances they are underneath the ocean in a dry enormous cavern.
  • Moltonia is a "world inside a world" with a blue sun which once abducted the Holliday Girls.

Fan Works

• Abraxas (Hrodvitnon): Titans can use tunnels cutting through the Earth's mantle to shorten global travel time, like Godzilla did in Godzilla: King of the Monsters (2019); but later chapters also hint that the real Hollow World ecosystem is located at the planet's core (here referred to by Ghidorah as the Realm Below, and mainly based off the Hollow World's portrayal in Godzilla vs. Kong), and the Realm Below is largely unexplored or untouched even by the Titans.

Film — Animated

• In the Ice Age film series there is an underworld which dinosaurs still roam, first seen in Ice Age: Dawn of the Dinosaurs.
• In Atlantis: The Lost Empire the location of Atlantis is in a humongous air pocket in a cave underneath the water, described as being like the grease trap of a sink.

Film — Live Action

• The movie The Mole People featured a team of scientists going down, down beneath the surface of the Earth to find another society of humans, along with the eponymous Mole People.
• The entirety of the MonsterVerse revolves around this:
  • The theory is referenced in Kong: Skull Island by Houston Brooks as a possibility to the origins of kaiju. Sure enough, Skull Island is located above some kind of fissure from which monsters like Skullcrawlers emerge. They may not be implying the whole planet is hollow, only that there is a large enough space underneath Skull Island for a whole ecosystem of ancient monsters to survive in.
  • Confirmed in Godzilla: King of the Monsters (2019) when Godzilla can use the underwater tunnels (which have very high-speed currents running through them) to pass from one ocean to another in record time without those pesky continents getting in the way. One character explains it and references Brooks' theory. We also visit Godzilla's lair in the Underwater Ruins of an ancient Godzilla-worshipping civilization, deep within those tunnels. How it got there, and who those people were, remains a mystery.
  • Godzilla vs. Kong confirms the existence of terrestrial Hollow Earth ecosystems as well, a massive jungle Lost World over which Kong reigns at the end of the movie. It also reveals that these zones are inaccessible to non-Titan surface dwellers by an inverted gravity barrier that requires specialized vehicles to cross.
  • The plot of the upcoming Godzilla x Kong: The New Empire is mostly set up in the Hollow Earth.
• Naboo in Star Wars: The Phantom Menace has a hollow core entirely filled with water.

Literature

• Against the Day seems to have this. It's unclear.
• In the Artemis Fowl series, the Fairies moved to inside the Earth in recent times — that or Beneath the Earth, depending on how you interpret it.
• In one of Isaac Asimov's stories in the rather epic Robots/Empire/Foundation chronology, some of the inhabitants of Trantor believe the universe to be an infinite mass of earth and rock, punctuated by occasional life-bearing bubbles. It is worth noting that the truth is more along the lines of Beneath the Earth, but only the (increasingly rare and alienated) scientific and technical elite still believe this, with the others believing such a belief to be a quite frankly bizarre conspiracy.
• Choose Your Own Adventure:
  • The Underground Kingdom had a star in the middle of the earth and an advanced civilization living inside of the crust.
  • Likewise in Through the Black Hole, in which the planets in the black hole appear to be spherical and smooth (and repel all other objects), but can be burrowed into with some difficultly to locate the lush wildlife and Sufficiently Advanced Aliens on the inside.
• The Death Gate Cycle.
  • The second book, Elven Star, features the world of elemental Fire as one of these, where all the stars in the sky are the equivalent of gigantic lighthouse beacons.
  • The world of elemental Water is another example, with the slight difference that the islands are floating in air-bubbles in a vast sea filling its volume, meaning that people travel around in submarines instead of airships.
  • Even the world of elemental Air apparently is this according to the map, even though the "walls" presumably consist of some kind of force fields rather than solid matter.
  • The final book implies that all the worlds exist in what used to be our solar system, and can be reached through mechanical rockets even after the Death Gate is closed — after you get through the planets' artificial crust, in any case.
• A variant in Nikolay Nosov's children's book Dunno on the Moon, where the Moon turns out to not only be hollow but actually housing a mini-Earth inside it. The only difference for the shorties (all people in the book series are shorties, small humans) living on the mini-Earth is that, at night, everything is dark. Some technobabble explains how they get any light at all during daytime (something about cosmic rays turning into visible light when passing through the Moon's crust). The Moon-shorties have no idea that they are living inside a planetoid, as they don't have rockets yet and, frankly, have no need to try to figure out how to get into space (being a thinly-veiled stand-in for Western capitalists, most Moon-shorties are greedy and corrupt and, as such, are uninterested in the advancement of their people; this is the first book where the concept of money is brought up, when an Earth-shortie goes to a restaurant and tries to leave without paying). Another big difference (that is actually a big plot-point) is that, while on regular Earth all fruits and vegetables are huge compared to the shorties (as it "bigger than the shorties" in some cases), all fruits and vegetable on the mini-Earth are in proportion to them. Thus, for those living on the mini-Earth, hunger is a real possibility. After explaining who he is to two Moon-shorties, Dunno tells them that their rocket on the Moon's surface is full of seeds of giant fruits and vegetables. The three of them try to market that idea and create a fund for building a rocket to get from mini-Earth to the Moon's surface and retrieve the seeds. Unfortunately, without "moonite" (an Expy of H. G. Wells's cavorite) that can only be found on the Moon's surface, building a rocket is extremely difficult, as shown by the second expedition sent from Earth (the rocket is much smaller and most of it is devoted to fuel; the first rocket, equipped with "moonite" only needed a little bit of thrust and was luxurious by comparison).
• In Fafhrd and the Gray Mouser, Nehwon is a concave hollow world.
• Foucault's Pendulum pokes fun at this trope, together with many others commonly believed by conspiracy theorists.
• The Future of Supervillainy takes place in one of these, full of dinosaurs, lost civilizations, and an eternally shining sun in the center of the Earth. It becomes a place where Gary is able to settle the refugees from a dead planet with the locals' permission.
• Godzilla: Discussed in Godzilla at World's End. Alexander Kemmering and his daughter Zoe are both convinced that a portal to the hollow world — which they believe is the Garden of Eden, and the birthplace of mankind — is due to open in Antarctica in 1992, and plan to be there when it does. Unfortunately, the expedition costs Alexander his life, while Zoe successfully enters the subterranean area and discovers a crystalline city, but has been driven mad by her experiences and takes control of it, along with the Ancient Ones who predated mankind. In late 2000/early 2001, she uses the monsters she's created there in an attempt to exterminate mankind, only to be thwarted through a combination of a team of humans (who enter the city and ultimately free the Ancient Ones from her control) and Godzilla, who also enters the area and does battle with the monster Biollante.
• In The Golden Transcedence, the agent of the Silent Oecumene claims that they live inside a black hole, which has been hollowed out and so exerts no gravitational pull on them.^DetailsSpecifically, they claim to have found a way to produce a second event horizon within the first, and so on, to produce a series of nested 'spheres'. They then populate each new layer as a way to provide nearly unlimited living and computational space. (The agent itself is viewed as being present in a field just outside a miniature black hole of its own.)
• In Robert Rankin's The Greatest Show Off Earth, our world is the inner layer of a hollow world (in a kind of matryoshka style). The inhabitants of the outer layer are planning to plug up the holes at the poles because they are fed up with our pollution spilling out.
• Great Ship: The Great Ship is a hollow starship about the same size as Jupiter. It has a hollow core large enough to contain an entire world, Marrow. The rest of the ship is full of thousands of fuel tanks that can fit moons, and even more caverns designed for habitation.
• The interior of Onyx in Halo: Ghosts of Onyx has a portal to one of these. Specifically, it's a Forerunner Shield World.
• Hollow Earth: The long and curious history of imagining strange lands, fantastical creatures, advanced civilizations, and marvelous machines below the Earth's surface by David Standish goes into detail on the fictions, theories, and wacky religions inspired by this trope, but even he doesn't bother listing all the stories based on this trope (it was, for example, quite popular in the 19th century to base utopian fiction inside a hollow earth).
• The Indiana Jones novel Indiana Jones and the Hollow Earth is about this. More specifically, Indy discovers Ultima Thule (see "Real Life" examples below).
• The John Gribbin novel Innervisions. This is meant to be a shock ending to the book, except the cover announces "The world was a sphere... and they were inside it!"
• Hell in Philip José Farmer's Inside Outside. According to some characters, it used to be flat but changed as scientific knowledge advanced. It's later revealed, however, that this is false and that hell is a space station.
• Journey to the Center of the Earth implies that there is a second sun at the core of our own planet, meaning we live on the outside of such a sphere. At the time, before the discovery of radioactive elements, this was one of several speculated explanations for the Earth's internal heat.
• The eponymous structures in George Zebrowski's Macrolife.
• The Shellworld(s) in Matter is essentially a nesting-doll series of these, although all the inhabitants live on the "outside" of each shell. What's on the inside? Why, artificial stars, some of which roll across the sky and some of which are fixed.
• In "Maureen Birnbaum at the Earth's Core", Maureen travels to a world inside the Earth, where she is captured by giant white apes who make her their priestess.
• Due to a combination of its gravitic and atmospheric oddities, the world of Mesklin in Mission of Gravity is thought by its inhabitants to be bowl-shaped. They're incorrect (it's actually a very flattened spheroid).
• More Information Than You Require features a long section on the mole-manic societies dwelling within the hollow Earth, including a list of 700 mole-man names and countless allusions to many of the other works listed on this page.
• The Narrative of Arthur Gordon Pym of Nantucket abruptly ends with Pym's ship falling into a giant hole at the South Pole. It's likely that the whole novel was a parody of travelogues, including this bit, as the "holes at the poles" theory was already becoming discredited by then.
• Edgar Rice Burroughs cemented the concept in pulp with Pellucidar, an internal world where he set several of his stories, including a notable crossover with Tarzan in Tarzan at Earth's Core. He also wrote The Moon Maid, in which the first spacecraft from Earth to land on the Moon discovers that it is hollow, with a living internal world that can be reached by descending through certain craters.
• The iconic example from Perry Rhodan would be Horror, a hollow world in six distinct layers that at least from the protagonists' perspective seemed to serve primarily as a planet-sized trap for unauthorized users of the recently-discovered intergalactic matter transmitter network connecting at least the Milky Way and the Andromeda Galaxy (plus some outliers) at the time. The "Mobys" from later in the same arc probably also qualify by virtue of being largely sleeping large-moon-sized anorganic lifeforms whose insides were frequently colonized by opportunistic aliens.
• In Prisoners of Power, the inhabitants of the planet Saraksh are convinced that they live on the inner surface of a spherical cavity, due to the unusual optical properties of its atmosphere (the horizon looks like it is above the observer).
• Richard Sharpe Shaver's sci-fi stories and related conspiracy theories revolve around a Hollow Earth ruled by a race of malicious technocratic Morlock-like creatures called "deros", who toy with humanity for their own cruel amusement.
• The short story "Shell" by Stephen Baxter is set on a planet that has been folded in on itself in the fourth dimension. There is no sky — people looking up see the other side of the planet curving over them, as if it's a shell. When one character uses a hot-air balloon to explore the other side, she witnesses the "shell" flatten out and then become curved normally, while the land she just left curves into a shell over the sky.
• Star Wars: Honor Among Thieves: The planet Seymarti has had its mantle completely emptied out; the crust is held up away from the core by incredibly powerful force fields left by the K'kybak. This is implied to have been necessary to generate the K'kybak's anti-hyperspace field. To keep said field out of the Empire's hands, Han disrupts the force fields and implodes the planet.
• Symzonia: A Voyage of Discovery by "Captain Adam Seaborn" is a 1820 novel which espouses ideas of John Cleves Symmes, Jr. and one of the earliest literary examples. Its other claim to fame is that was among the sources which inspired short story MS. Found in a Bottle and novel The Narrative of Arthur Gordon Pym of Nantucket by Edgar Allan Poe.
• The BookWorld in the Thursday Next series eventually reboots and turns into one of these in One Of Our Thursdays Is Missing. Used to be the various books were essentially pocket worlds floating in space independently of each other, only connected by a library acting as a dimensional nexus of sorts, but they now occupy the surface of a hollow world, with the various subdivisions of literature — Fiction, Poetry, Mythology, Non-Ficition, etcetera — each occupying a single continent.
• In The Time Ships, the time traveler returns to the future once again, but finds it changed. The Morlocks are now "good" in this future, and are also incredibly advanced, having engineered a hollow sphere around the Sun slightly inside Earth's orbit. Morlocks live on the outside of this hollow sphere in the dark, while the Eloi live on the sunlit inside of it.
• In the Tunnels series, the Earth's core is hollow and contains an Eden-like paradise called "The Garden of the Second Sun".
• In Wall Around a Star, the inhabitants mainly lived on the outside of the Sphere (or in the various layers of the Dyson Shell).
• The White Darkness. A girl is dragged along by her eccentric uncle to find the entrance to the hollow earth in Antarctica. He's wrong, and quite insane.
• In The World and Thorinn, there are many worlds within the Earth with the lower ones having less of a pull of gravity due to almost as much material being overhead as underfoot.

Live-Action TV

• The Babylon 5 station could technically be considered a "world" of this sort, but there's a reason for this. The station is a design called an O'Neill Cylinder. By rotating along the cylindrical axis, the reactive centrifugal inertia produced along the inner surface becomes an artificial gravity. It was the best way humanity had at the time for producing artificial gravity; they didn't gain access to alien-based gravity generator technology until after 2261 (Season 4).
• Doctor Who: "The Pirate Planet" gives this an interesting twist. Zanak is a gigantic hollow planet with enormous transmat engines at its core. It can literally materialize around smaller planets and squeeze them of their wealth and energies.
• The Clock Punk opening sequence to Game of Thrones takes place on at the very least a parabolic version of the world map of Westeros and Essos with an astrolabe floating above it functioning as both the sun and the Title Card for the show.
• Lexx's planet Fire has an inner surface with inexplicable bright daylight and Earth-normal gravity. Given its supernatural nature, one can only shrug.
• In Sanctuary it turns out that the Earth really is hollow, and populated by technologically-advanced humans and Abnormals who migrated underground in order to escape the vampires ruling the world in the past. And the only people that knew were Jekyll and Hyde.
• Such worlds turned up in Star Trek: The Next Generation and Star Trek: Voyager. The TOS episode "For The World Is Hollow And I Have Touched The Sky" had a variation, a shell covering an artificial planetoid to hold the atmosphere in.

Podcasts

• In Jemjammer Kofuspace is a sphere (essentially a solar system) composed entirely of solid rock — or at least the rock-like material covering the outside of a sphere. Inside, every planet is actually a concave bubble inside the mass.

Tabletop Games

• The Dark Eye: Downplayed with the discontinued world of Tharun, which was actually an alternate universe (with its own gods and celestial bodies) whose only gates were reached through deep caverns. So it felt like a hollow earth, although it wasn't.
• Dungeons & Dragons:
  • The Hollow World is a game setting inside another game setting, being located inside the planet on which Mystara is set, reachable by huge holes at the planetary poles. In-universe, it's used by Immortals (the gods of the setting) as a sort of ark for creatures and cultures that would have gone extinct in the surface world, including dinosaurs, Kogolor dwarves (the surface-dwelling pastoral ancestors of the more stereotypical main setting dwarves), beastmen (the bestial ancestors of evil humanoids like orcs, goblins and ogres) and advanced Lizard Folk, with a few floating continents for flavor.
  • Spelljammer got Herdspace described in The Maelstrom's Eye by Roger E. Moore — a crystal sphere with an internal surface (the size of a "small" solar system) covered with inhabitable landscape, much like a naturally-occurring Dyson Sphere.
  • The World Builder's Guidebook, a supplement for 2nd Edition D&D, discussed variant World Shapes, including hollow worlds. Notably, it points out that the same blank globe-maps it provides for Earth-like spherical worlds are also perfectly usable for a hollow sphere.
• Genius: The Transgression has the Hollow Earth as one of its many bardos — pocket realities created when established science is proven wrong. From the presence of things like "brontosaurs" and Piltdown Men, it's implied to also be a catch-all for every paleontological blunder ever committed. It's also been recently taken over by Nazis — to be precise, Manes (creatures and people created in the same way bardos when an established theory or philosophy is abandoned) formed at the end of WW2 when the real Nazis were crushed and almost all faith in their ideology crumbled.
• Hollow Earth Expedition is all about this, using the fluidity of the pulp genre to meld the hollow earth with Thule, Atlantis, and prehistoric times, and any sort of lost civilization, and the whole thing is discovered on the cusp of World War II. Hey, how else are you going to feed Nazis to dinosaurs?
• Magic: The Gathering: The plane of Mirrodin is hollow, mostly metallic, and has five suns - one for each color of mana. Instead of orbitting it, they travel through five channels, called lacunae, that descend into the plane's mana core.
  • When the plane was taken over and reforged by New Phyrexia, Elesh Norn created nine separate layers or "spheres" nested inside each other. The outside is the Glorious Facade covered in monuments to the Praetors' victory, then the Mirrex is a barren wasteland where the remaining Mirrans try to eke out survival, then a layer dedicated to each of the five praetors and their manifestos, then the Mycosynth Gardens that serve has a protective layer around the Seedcore where Norn is growing her invasion tree.
• Pathfinder:
  • Deep Tolguth is a vault in the Darklands, complete with otherwise-extinct animals. It's more like a country-sized mini-world than an actual hollow planet, though; an ancient terrarium made by Sufficiently Advanced Elementals.
  • The Outer Planes are arranged in a cosmic take on this trope known as the Outer Sphere. They are laid out on the inner surface of an unimaginably large sphere, with the Inner Planes — the material world, the ethereal plane and the elemental planes — in its precise center. The surface of the Outer Sphere consists primarily of the Maelstrom, a vast expanse of ever-shifting chaos and unshaped matter, with the other Outer Planes as isolated "continents" surrounded by the Maelstrom's "ocean". Heading deep enough within the Maelstrom or underneath one of the other planes eventually leads to the Abyss, also called the Outer Rifts, a seemingly infinite system of abysses and worlds-sized caverns extending in all directions.
• Warhammer 40,000: There are some mentions in the background material of hollow worlds, with the most prominent being the forge world Lucius. The interior surface of this wonder of the Imperium is covered by massive factories powered by an artificial sun of mysterious origin that sits at the planet's core.
• The World of Synnibarr roleplaying game's titular planet is hollow. According to the backstory, Earth's sun was becoming unstable, and because Earth itself was physically unsuitable, the planet's stellar engineers took Mars and expanded it, hollowed it out, and terraformed it until it was completely unrecognizable to serve as a new home for the evacuated human race. Overlaps with That's No Moon, as a suitably huge power generator was installed in Synnibarr's core to power the artificial planetary heating and atmosphere systems as well as the engine designed to propel the planet to a new star system to take up orbit in. After dozens of catastrophes, wars, and invasions during the 40,000 year journey, the inner core of the planet was abandoned, with the planetary machinery almost completely inaccessible at the top of a thousand-mile high mountain ascending to the planet's geographical core.

Toys

• BIONICLE: The early stories take place in a universe that is entirely contained within the body of their creator god.
• Masters of the Universe: Eternia is a hollow planet with an entire "Subternia" existing below its surface, with a multi-armed giant in the center holding everything together.

Video Games

• Aion: Atrea was hollow, with the Tower of Eternity through the center as the manifestation of the god Aion who provided the inside of the world with heat and light. However, after the Cataclysm, the center of the tower and a good deal of the planet's equator were destroyed leaving an apple-core shaped world held together only by magic. Although the planet orbits a nearby star, only one half of the planet gets any light from the star.
• In The Darkside Detective, Dooley believes in several different Hollow Earth conspiracy theories simultaneously. It's not said whether any of them are actually true, but the general standard of the other conspiracy theories Dooley believes (e.g. "The government is a mass delusion caused by chemicals secretly put in the water supply by the government") suggests that it's unlikely.
• The Descent DLC for Dragon Age: Inquisition reveals that Thedas has at the very least shades of this. The DLC's plot leads the Inquisitor and their party far, far below the Deep Roads, which are generally considered the deepest explored reaches of the setting, into a fantastic underground world of gigantic caverns full of bioluminescent life and even a lost ocean. It's also home to an entire lost clan of creepy dwarves wielding insanely advanced technology, and the Titans, absolutely humungous lifeforms whose mere movements trigger earthquakes on the surface, and whose blood is lyrium, the substance all surface magic is dependent on. The Inquisitor only explores the uppermost reaches of a Titan, implying the sub-Deep Roads cave systems descend even deeper into the planet, possible to the very core.
• Dragon Quest IV: The final area. Also used in Dragon Quest III where one of the big plot twists is The Reveal that the first two games took place inside an alternate Earth.
• Dwarf Fortress: The game world may or may not be spherical, but it's hollow alright, as your dwarves may discover the hard way. Specifically, it has a sort of "Swiss cheese" layering of an unmineable rock called slade which is covered in semi-molten rock and adamantine, depending on where.
• Final Fantasy:
  • Final Fantasy IV. It has a unique configuration in that, instead of two habitable surfaces opposed to each other, the Underworld IS the basic, solid planetary sphere, while the Overworld encases it. As proof, the Tower of Bab-Il rises from the Underworld and continues upwards through the Overworld. The Underworld is also considerably smaller, and, being located between the solid sphere and its shell, it lacks a Sun. The magma flowing through it is more than bright enough to do the job, though.
  • Final Fantasy IX: Gaia is revealed to be this, with Terra being the inside world. Originally, Gaia and Terra were each normal "life exists on the surface" planets, but Terra's incomplete merging with Gaia resulted in it getting tucked inside Gaia's core, with the area you visit near the climax being on the flip side of Gaia's crust.
  • Final Fantasy XIII mostly takes place on Cocoon, a Hollow World roughly the size of North America were it rolled up into a ball. Humanity resides on the inside surface area of the sphere, which is comprised of several distinct landmasses and oceans, and a giant freaking hole to nowhere. Cocoon floats in the lower atmosphere of Gran Pulse, a planet somewhat larger than Earth, given the apparent scale of Cocoon in comparison to it. Nothing about Cocoon makes sense scientifically, but it works anyway thanks to a million-some Physical Gods forcibly willing it to do things like float above Gran Pulse and have a functional atmosphere, gravity, and a day/night cycle.
• In Halo, Forerunner shield worlds are this combined with Dyson Sphere. They were designed to shelter their inhabitants from the Flood.
• Xardion has the Hollowsphere (Zikar), which is icy on the outside and jungle on the inside.
• Outer Wilds has Brittle Hollow, which is Exactly What It Says on the Tin: a thin crust of stone plates that's empty in the center, and which becomes riddled with gaps as chunks of magma expelled by its volcanic moon batter it. Justified because there's a black hole at its core, which the Nomai left unattended for thousands of years.
• The Secret World features a transit network between the various locations across the world, built into the depths of the hollow earth; known as Agartha, said transportation is based around the roots of the World Tree itself, and is attended to by a number of hulking Golems and one eccentric Victorian stationmaster.
• Septerra Core takes place on seven massive continents or "Shells" whose orbit and level are controlled by a central core with mythical wish granting powers.
• Shin Megami Tensei III: Nocturne: At The End of the World as We Know It (roughly 30 minutes into the game), the city of Tokyo becomes the new world, with the central "sun" waxing and waning every few days.
• Star Fox: Macbeth from the original game is stated to be a hollow planet, but in truth there is a core, albeit smaller than the crust that surrounds it. This makes a huge series of caverns that runs through the entire planet. Andross had plans to turn Macbeth into a massive base. The actual level even takes place with the Arwings flying around inside the planet.
• Super Mario Galaxy and Super Mario Galaxy 2:
  • Some of the planets in both games resemble hollowed-out spheres covered with huge holes and with a black hole underneath. If you fall into the black hole, you die.
  • The boss battle against Kingfin takes place inside a hollow planet, and the final battle against Bowser is inside a hollow Sun.
  • The Spin-Dig Galaxy level from Super Mario Galaxy 2 appears to be located inside one of these.
• Super Robot Wars: The world of La Gias (only visited in the Gaiden Game Lord Of Elemental, but referenced throughout the series) is like this. Its specifically in the center of the Earth, but its more of a magical dimension.
• Tales of the Abyss: The end of the first arc shows that underneath Auldrant's surface lies the Qliphoth, a mass of toxic liquid where the only lands remaining are two small islands holding Yulia City and the Tower of Rem, respectively. It's revealed that the Outer Lands used to be part of the Qliphoth, but that they had been raised up aeons ago to escape the miasma. And the Outer Lands are starting to crumble and fall, leading to the party having to lower the Outer Lands back down to prevent more casualties.
• Terranigma has this at the beginning, and later the protagonist drops through a hole to find himself on the surface of Earth.

Webcomics

• Axe Cop features a civilization of people living within the Moon rather than on its surface. The Moon Ninjas come from here.
• In Homestuck, the Battlefield has a very thick crust with a hollow center housing THE TUMOR (before it was removed) in its center.
• Reptilis Rex is based on the premise that Hollow Earth is real and that the Lizard Folk living in the center are forced to leave and integrate into human society with limited success.
• Schlock Mercenary has the Buuthandi, built by the F'sherl-Ganni. Due to math they're rather more like spherical solar sails counterbalanced with living habitats (drastically reducing the living space compared to a standard Dyson Sphere — only a few hundred thousand times Earth rather than millions), but allow them to tame an entire star as a source of energy and mass.

Web Original

• The Hollow Earth Insider
• PsyPets has this as part of its Framing Device; you're a volunteer working for the Hollow Earth Research Group (HERG). However, "Hollow Earth" in this setting is not actually inside Earth; rather, it's just a name given to an alternate dimension because the researchers were reminded of the old myth. References to the actual "Hollow Earth" pop up sometimes, though.
• What Curiosity in the Structure: The Hollow Earth in Science by Duane Griffin, is a short historical paper surveying scientific thinking about the hollow earth up to the present day.
• Orion's Arm has several different types.
  • Freespheres are small and light enough that they lack gravity, being essentially air-filled bubbles. That said, the largest ones can reach diameters of 5000 km, so they can certainly be considered worlds. These are used for zero-g recreation or (for those adapted to zero-g) as places to live in.
  • Gravity balloons are similar to freespheres except that they have a layer of asteroid rock on the outside: the weight of the rock counteracts the internal air pressure.
  • Ederworlds are even bigger than gravity balloons, being much larger than even gas giant planets. They're filled with a lightweight gas like hydrogen, which allows the incredible sizes. Unlike the previous examples, the interior of ederworlds isn't used for habitation, just the surface. Note that these are based on the bubbleworld design, which is mentioned below under Real Life.
  • Then there's Symme's Worlds, which differ from the previous examples in that most of them have openings at the poles to allow mixing of the outer and inner atmospheres. Most of them also contain luminaires, essentially artificial suns, to illuminate the inner surface.
• In The Salvation War, Heaven and Hell are both Hollow Worlds. This is partly due to the linguistic convention of saying that one is "on" earth but "in" hell or heaven. They have Alien Geometries in other ways as well; traveling in what appears to be a straight line on them results in a curved path.

Western Animation

• In Inside Job, every conspiracy theory is true except Flat Earth, which was a bet by employees of the Evil, Inc. running the world about the dumbest thing they could get people to believe. Instead, the Earth is hollow with a race of sapient hallucinogenic mushrooms living inside of it. One such mushroom, Magic Myc, is one of the main characters.
• The Simpsons: In "Bart vs. Australia", the Hindu god Vishnu is seen in the center of a hollow Earth, apparently controlling the universe from there.
• Storm Hawks: It's revealed in one episode that there are underwater cave systems that extend all the way down to the core of Atmos, and beyond that to the mysterious Far Side on the other side of the planet.
• The eponymous Slug Terra (incidentally, made by same studio behind Storm Hawks) is a vast, lush, and thriving hollow earth over 100 miles beneath the surface, populated by a variety of intelligent slug species with unique hidden powers, as well as other non-human races.

Real Life

• As alluded to above, this was an early theory of the Earth's structure dating back to the 1800s. And like the flat earth theory, some people on the fringes continued to advocate it.
  • The Theosophical Society were believers — their philosophy held all religion to have some virtue, all races were equal and they would promote studies in science, philosophy and religion. Popular through the early 1900s.
  • The Thule Society were less charitable — their beliefs influenced the Nazi doctrine of Aryan supremacy and Nazi mysticism.
• As recently as 2007, some guy got some attention for his fundraising for an expedition to the poles to enter the holes to the hollow earth supposedly located there.
• An unfalsifiable (and therefore scientifically irrelevant) claim is that the Earth is in fact a hollow sphere; in this model, we're currently living on its inner surface and the rest of the universe fills its inside volume, with space distorted so that the further in you go, the smaller you get.
• David Icke believes this is where the Nazi leadership escaped to. He also believes that the holes are enormous and that's why commercial planes never fly near the poles. (Planes frequently fly over the poles as a way to cut down on travel times. It's easier to fly to Russia from Canada by flying over the poles than going west.)
• Edmund Halley (of Halley's Comet fame) was one of the earliest proponents of the Hollow Earth as a scientific theory rather than a legend or religious belief. He speculated that Earth was made of several hollow spheres (akin to Russian Nesting Dolls) that rotated independently of each other. He came up with this theory as a way of accounting for variations in the behavior of magnetic compasses; his idea was that something below the surface (the aforementioned spheres) was causing interference. (To be completely fair, it's not that far off from the modern theory of a dynamo generated by a rotating liquid core.)
• In the 1820s, Hollow Earth proponent John Symmes lobbied the United States government to fund an expedition, arguing that the U.S. could conduct valuable trade with the people living inside the Earth. President John Quincy Adams was convinced, but the project was cancelled by his successor, Andrew Jackson. Due to to Jackson's lack of formal education and hillbilly image, it's been joked that he canceled the expedition due to believing the Earth was flat.
• The closest (known) Real Life things to a hollow world are Saturn's moon Hyperion, an irregularly shaped body that is said to have a 40% of its volume as empty space, and similar rubble piles as Mars' largest moon Phobos.
• Some proposed designs for space habitats would fit this trope. Possibly the largest one is the bubbleworld, a relatively thin shell around a huge "bubble" of a lightweight gas such as hydrogen. This could potentially have a diameter of 240,000 kilometres, several times that of Jupiter, yet have just 3 times the mass of Earth as a result of its low density. On the other hand, gravity at the surface would be very weak for the same reason.
• The Hollow Moon theory claims exactly that, it being some sort of alien humongous starship parked in orbit around Earth for unknown reasons.

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