This Florida sinkhole hides a rainforest-like micro-environment in its depths.

The superstar of Cold War nuclear bunkers has been featured in countless films but is now barely operational.

Sail through this subterranean show cave that is home to a legend that would go on to name nearly everything around it.

This unmarked and unloved Manhattan subway grate created one of the most iconic images in American cinema.

A mysterious monument meant to be a guide into "an Age of Reason" was destroyed after an apparent bombing.

The "Seinfeld" diner.

This futuristically sylvan church is a glass-enclosed marvel of modern architecture.

This 4,000-foot-diameter hole is touted as "the most well known, best preserved meteorite crater on Earth."

A DIY art gallery/music venue/lecture hall dedicated to video game culture.

Home to items never before seen by the public.

This Boston medical museum features the skull of the famous medical case of Phineas Gage.

This beautiful building in the heart of Manhattan's Financial District was empty for decades.