Brace yourself for the slowest, scariest, most spectacular drive, down the Drakensberg Escarpment.

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

An architectural marvel that dates back to the zenith of Indian architecture.

This underground cave located in the most barren reaches of Idaho is filled with ice year-round.

A lava tube cooled to form this long tunnel that stays chilly even at the height of summer.

An underground spring in a labyrinthine cave system, decorated with stalagmites and stalactites.

The top of the holy mountain for the ancient Spartans looks like a pyramid—is it man-made or a natural phenomenon?

This restaurant serves wood-fired fare served in a natural cave with a live spring.

The only runway directly into the magic kingdom has been closed since 1972, but it still sings to you if you drive fast enough.

This canyon is named for a unique geologic formation where the river vanishes underground near the mouth of the canyon and reappears farther down.

The Grand Canyon of Texas.

The eerie ruins of an isolated abandoned town nicknamed "the Widowmaker" for its deadly gold mine.

Narrow slot canyons in a badland eroded into soft sedimentary rock provide an otherworldly landscape in this remote Nevada state park.

This small turbine mill along Rocky Creek was built in 1928

One of the few Cold War-era bases with many of its original structures still standing.

The last remnants of a lakeside airport that was bulldozed overnight by the mayor of Chicago.

A site of pagan worship which still attracts people looking for fairies.

Built in 1925, this glass-roofed shopping arcade is known for its modernist Italian architecture.

Every winter, this former planetarium is transformed into a massive, brightly-lit Christmas ornament.

The internet as provided by a James Bond villain.

Dug as a secret royal escape route, the tunnel became a wartime bomb shelter and dumping ground for vintage cars.

A Victorian Fort built into the chalky cliffs that overlook the English Channel.

An expansive complex of subterranean tunnels is all that remains of one of Europe's most formidable medieval fortresses.

This small museum houses rare airplanes from aviation's golden age.