A Texas cave network is home to some of the world's most spectacular-looking and bizarrely named mineral formations.

Vienna's underworld of tunnels and subterranean rivers made an iconic appearance in a 1949 Orson Welles film.

The subterranean "lake" below the Paris opera house inspired the Phantom of the Opera's lair.

Exquisite wall sculptures carved in secret by an early quarryman in an obscure corner of the Paris Catacombs.

A tiny theater hidden in an alley plays a constant stream of short silent films for anyone willing to peer through the peephole.

A Lycian city of the dead carved into the hillside of Southern Turkey, complete with startlingly human touches.

An unfinished tomb carved into a giant boulder in the Arabian Desert.

A whimsical village of unique treehouses resides in a Washington forest.

A real-life replica of a home from Hayao Miyazaki's beloved movie "My Neighbor Totoro."

Hidden in plain sight on a pair of Manhattan subway tunnels are a pair of public instruments that sing to each other.

Ride the subways of yesteryear.

Mysterious 500-year-old tapestries depict a unicorn hunt.

The one-stop shop for all of your superhero (or evil arch-nemesis) needs.

A room in New York City that contains 250 cubic yards of dirt worth a million dollars.

A pedestrian island in the middle of world-famous Times Square emits a strange (and purposeful) humming noise.

More gold than anywhere else, ever.

The oldest surviving bridge in New York City, which reopened to pedestrians in 2015.

A natural gas leak provides a flickering flame beneath a waterfall.

New York City's smallest piece of private property.

Become a prohibition rebel.

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

A Pythagorean funhouse that tries, successfully, to prove that math is the coolest thing ever.

A miniature rainforest is growing inside of a Midtown Manhattan office building.

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