A fiery crater has been burning in the Karakum Desert since 1971.

A stealthy Apache hideaway that became the haunting site of a mass grave.

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

Visit this playground of waterfalls, caves and sinkholes.

In a long-dry lake bed, these groups of massive stone pillars bear a striking resemblance to clumps of everyone's favorite fungi.

The largest cave shaft in the world is home to thousands of birds and popular with BASE jumpers.

Marking the ancient boundaries of asylum around Beverley Minster.

Lewis Carroll's White Rabbit or something else altogether?

A metal tree emits eerie, melodic notes on top of Lancashire's Crown Point.

A modern English garden of eccentric beasts, follies, and oddities.

Astonishing rock formations dot the Brimham Moor landscape.

Once thought to be the mysterious work of a witchy prophetess, a well with unusual properties turns objects into "stone".

Mile-long cave system near Great Smoky Mountains.

Enormous lake at the bottom of a unique cave system.

The "World's Largest Underground Business Complex," a 55,000,000-square-foot city underneath Missouri.

A salty cave excavated by elephants and the location of a deadly disease vector.

An ethereal glowing blue ocean cave in Croatia.

A tunnel of hardened lava along Maui’s famous Road to Hana.

Bizarre Cavern.

These curious caverns have been home to mushrooms, gangsters, and disco.

Salt cured mummies continue to turn up in this Iranian mine.

Tubing through a cave lit with glowworms is a magical underground experience.

Self-sufficient greenhouse floating on the Hudson River.

America's only nuclear missile silo open to the public.