Tear Jerker / The Mysterious Cities of Gold

• Right off the bat, we get the death of Father Rodriguez, a good man who raised Esteban since he was a baby, and the closest thing that Esteban had to a father. Esteban's reaction and the gorgeous (but sad) music turn the death of a minor character into a huge Tear Jerker.
• The Sinking of the Solaris: In order to save his friends from being captured by the Spaniards, Tao is forced to destroy the Solaris, one of the last (or so it seems) relics of his people.
• The Heroic Sacrifice of the High Priest of the City of Gold, who we have only just discovered to be Esteban's Disappeared Dad.
• The death of Zia's father Papacamayo just after they'd finally been reunited after years apart is also sob-inducing.
• From season two, there is the very likely death of Mayuca from season one and Esteban finally learning his father's fate.
• In season two Esteban has just learned that his father is alive, but very ill and contagious, to the point where he cannot even give his father a hug. And if that wasn't enough, Zares captures his father to use as leverage to force the kids to find the other Cities of Gold.
• The first episode of season 3 has the Condor falling into the sea due to an earthquake. Although it later turns out to be alright, the initial impression is that the Condor has been destroyed, like the Solaris before it.