This astonishingly geometric cave has inspired everyone from Jules Verne to Pink Floyd.

A 1,500-year-old, 3-story subterranean city where ancient Persians took refuge in times of war.

Whitewashed mosque contains the world's largest carpet.

This enormous sports car themed amusement park is home to the world’s fastest roller coaster.

Planned as the world’s first zero-carbon city, it had lofty ideals—but is only 5 percent completed and aiming for 50 percent carbon-neutral.

This indoor ski resort has a mountain contained inside a mall.

A record-breaking pool that uses computers to turn ocean water into cleaner, private swimming water.

Australian Lake set aglow by Noctiluca Scintillans.

An Australian lake whose pink hue defies scientific explanation.

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

An immersive environment that is part haunted house, part choose-your-own-adventure, and part jungle gym.

On the Oregon coast there is a natural hole that seems to be draining the sea.

World's first "penitentiary," meant to be humane, drove men insane.

A psychedelic labyrinth on the San Francisco bay.

Roman ruins top white travertine terraces formed by ancient hot springs.

These tombs were built into the side of a mountain so that ancient angels could reach the dead.

In this historic region, homes and churches are carved into ancient volcanic rock formations.

Holy Hindu shrine in an enormous, monkey-filled limestone cavern.

Robot jockeys ride their humped mounts to victory as part of a 21st-century twist on an ancient desert sport.

Step into a cartoon at this Seoul café that aims to evoke a two-dimensional scene.

Plenty of old carney magic still haunts this photogenic amusement park.

Secret North Korean passage discovered below the world's most dangerous border.