Human-made caves excavated to hide a secret society of wealthy pagans.

Fantastically decorated underground chambers built in the 1760s.

This former Masonic lodge has been transformed into part museum, part bar, all awesome.

You can spot this teeny tiny stained-glass window from the Bonifacius bridge.

You would never come across this tiny green oasis if you didn't know it existed.

This small corner bar is home to a rare 1930s dance organ that still plays tunes for one Euro.

An enormous, inside-out glass globe built in 1935.

Yale University's home for rare works, including the mysterious Voynich Manuscript.

This once-forgotten oasis in the middle of Lisbon was first created over a century ago quite by accident.

A king's pet, a pope's gift, an artist's inspiration, and a tragic shipwreck.

A beautiful and abandoned New York subway station from 1904, complete with chandelier.

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

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

This lower Manhattan bar is set up in an old bank vault that rests beneath a skyscraper that hides even more historic splendor.

Elevated freight railway turned wildly successful urban park.

Amid the bustle and noise of the Financial District hides a secluded garden oasis above the city streets.

Dodge prohibitionists and slide through the telephone booth in Crif Dogs.

The Cambridge pub where Francis Crick announced that he and James Watson had discovered the DNA double-helix.

The television series' iconic giant foot was borrowed from this classical painting.

A makeshift shrine to the late rock star is still kept up on the nondescript façade outside 1 Logan Place.

In this cobwebbed old operating theater, you can practically hear the screams of the unanesthetized patients.

A special shop catering to the needs of things that go bump in the night, and also helps kids become writers.

A subterranean ice warehouse that has lain hidden beneath central London for over a century is now open to the public.

A tongue-in-cheek arcade where the games are based on everyday life.