Following the trail of an old metro line, this scenic path is haunted by a creepy spriggan statue.

Wondrous sandstone hoodoos where Native Americans collected clay for pottery, 9,000 years ago.

Erosion and time have created a naturally-formed water park.

Hidden behind musical flora and forgotten for over a thousand years, this cave is now a neon dream.

Semi-precious Blue John stones have been mined in this cavern system for centuries.

Mosaics, storks, and brothels—this ancient city has it all.

Terrapins of all colors and shapes are quick to bring fascination (and possibly long life) at this museum.

An unfortunate geological resemblance to Satan has labeled this Pasadena gorge as a passage to the underworld.

An undulating wicker beast looms peacefully atop a sand dune in Belgium.

A contemporary art installation housed within a Gothic cathedral.

An Italian crevasse filled with abandoned buildings gives visitors a look at the world without humans.

These numerous Israeli caves were dug out over hundreds years for reasons ranging from hideouts to burial sites.

This massive subterranean fissure is known as the "underground Grand Canyon."

A wonder of natural limestone formations etched by millions of years of natural interaction between rainfall and rock and air.

Caves that can't seem to quit producing the remains of prehistoric humans.

Cave on extinct volcano, once home to famous mathematician Pythagoras.

A miniature train-ride through Slovenia's largest cave system.

This popular tourist cave was ignored for almost 200 years before being mined into an attraction.

Take a drunken tour inside the world's largest known geode.

A cave's rare beauty held a cavernous secret hidden underground.

This complex of vertically-excavated Buddhist, Jain, and Hindu monolithic temples in India's Maharashtra providence illustrates a spirit of tolerance characteristic of ancient India.

Rock-cut cave complex filled with ancient Buddhist artwork.

The world's longest known cave system.

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