A unique rock formation that only a few have managed to venture inside.

Stuck in a bygone era, the oldest subterranean shopping street in Japan hides beneath the popular Asakusa district of Tokyo.

A sinkhole and now a swimming hole, too, full of dazzling turquoise water.

A beautiful discovery site of prehistoric burials.

A cave network located at the southernmost tip of mainland Greece was once believed to be an entrance to Hades.

Stepping away from the glitz of mobsters and casinos to learn about the other history of Vegas.

A luxurious doomsday bunker hidden beneath an unassuming Las Vegas home offers the best of subterranean suburbia.

Folklore says this medieval fortress was plopped atop a portal to hell to trap the demons below.

After 400 years of being closed to the public, this monastery's underground tunnels and secret garden are now a museum.

A centuries-old forgotten underworld lies beneath Malta.

All you ever needed or wanted to know about America's favorite whiskey, but not a drop to drink.

The oldest known metal-mining site in England dates back to the Bronze Age.

A natural sandstone bridge hidden in the Sewanee forest.

A natural swimming pool in the middle of the Carite Forest.

At 705 feet high, Brazil's "House of Stone" is the largest cave mouth in the world.

Home to an endangered salamander, a full moon celebration, and a large spring-fed outdoor swimming pool.

This set of Berber granary caves is now an interpretation center for the cave window structures in the Clarino valley.

This human-made cave is one of the many snow storage chambers that supported the ice supply industry in the Sierra Mariola area.

For many years, the origin of these enigmatic artificial caves was the subject of debate among historians.

Hidden in an enchanting ravine, numerous mysterious sandstone grooves hint at ancient pagan rituals.

The remains of a 37,000-year-old prehistoric society were discovered in this mammoth cave, one of the largest in Asia.

The largest medieval water tank on the Iberian Peninsula is preserved beneath the Cáceres Museum.

A deeply beautiful 15th-century stepwell with a tragic story.

Thousands of exquisitely carved stone water storage wells, hundreds of stone steps fill this exquisite medieval stepwell.