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

An emerald-green grotto just a short trip from Austin.

A harrowing trail up a mile-high mountain.

A 10 million-ton rock once worshiped by the Tahamies Indians, accessed by an astounding staircase.

Once thought to be the oldest living tree in the world, Methuselah was germinated before the Egyptian pyramids were built.

A chain of 16 wondrous lakes formed as a result of the gradual dissolution of soluble layers of bedrock.

Snow-capped peaks, colorful waterfalls and stunning vistas on the edge of the Himalayas.

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

A lake with hundreds of ancient skeletons surrounding it. The surprise is what killed them.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

The demolished ruins of a poorly located Japanese Love Hotel.

A cemetery with goat-horn bedecked gravestones.

A colorful Peruvian city of the dead.

Catalonia Tradition: Beating the hollow Christmas log until it defecates in your fireplace.

An explosion of natural color known as "the river that ran away from paradise."

Exact replica of the ancient monument, but much, much lighter.

Aqueducts have dramatically changed this old lake, now home to tufa towers and its very own species of tiny brine shrimp.

This "dead marsh" sits among the largest sand dunes in the world, a forest frozen in time.

Natural time capsule containing an alien ecosystem.

A salty red wasteland in Tanzania is a breeding spot for endangered flamingos.