The Oldest House

Despite the fact that it's a giant featureless slab of concrete taller than most skyscrapers in the middle of one of the most populated cities in the world, no one seems to notice or acknowledge it. The Bureau (who specializes in these sort of anomalies) didn't notice it until they discovered it by complete accident in The '60s and since then the Bureau has been using it both as a Headquarters, a lab and a containment area for its anomalous content. Notably, this Perception Filter started extending to the FBC's own activities, letting them requisition funds from the government that wouldn't ever get questioned or audited so long as they were reasonable.

Example of:
Perception Filter