The unique waterfall in Iceland's south features a backdrop of geometric black lava columns.

Hidden in a high mountain cave, this hermitage dates back to the ninth century.

An underground paleo-Christian burial site composed of the remains of several cemeteries and Basilicas.

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

A 140-year-old castle with underground caves hidden in San Francisco.

The island houses the ruins of a secret nuclear fusion lab that once employed high-profile Nazi scientists

With its vast selection of books, comics, and records, this nearly 70-year-old open-air market always rewards the patient browser.

"Di amigo y entra" at this Argentinian Middle Earth-inspired pub.

Crumbling crypts and overgrown graves rise just out of arm's reach in this forgotten Buenos Aires graveyard.

A gateway to a mysterious network of underground tunnels.

Stenciled handprints and wall paintings dating back 10,000 years, some of the earliest forms of cave art.

A series of waterfalls so massive they straddle the border of Argentina and Brazil.

This historic, palatial theater is now one of the world’s most beautiful bookstores.

An underwater restaurant, surrounded by a coral reef.

Fine dining 20 feet below the surface in the Indian Ocean.

Bioluminescence in the reefs of the Maldives causes the sea to glow like a starry night sky.

This picturesque medieval monastery guards a small trove of historic treasures.

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

This small group of sand dunes manages to pack in a strange rainbow of colors.

A breathtaking viewing platform over the Alps.

Artfully arranged bones of 5,800 Austrians.

Swarovski's museum/theme park is a fake diamond fantasia overlooked by a giant.

The crypt of the imposing Stephensdom holds royal intestines and thousands of skeletons.

The beautiful baroque library of the Hapsburg empire.