Abandoned tunnels dug for the once-thriving sea salt industry on the coast of southern Spain.

The ruins of an ancient stadium that hosted gripping chariot and horse races.

New York's oldest and possibly grandest keeper of books.

A Texas cave network is home to some of the world's most spectacular-looking and bizarrely named mineral formations.

Things roll uphill on this Mexican street that seems to defy gravity.

The lab where the scientist made his groundbreaking discoveries is preserved on the basement floor of the Faraday Museum.

The remains of this RAF plane and its crew were lost for decades, nearly engulfed by the Malaysian jungle.

This hidden stream beneath Indianapolis makes an appearance in the best-selling novel "Underground Airlines."

Thanks to a spelling mistake this bizarre beaver-tiger hybrid became the symbol of a Siberian town.

A spooky juxtaposition of caves and graves gives this legend-filled cemetery a particularly haunting vibe.

Western Europe's only representation of a Roman goddess still in its original location sits in an unassuming park.

Forgotten under the construction of a new urban roadway is a small, abandoned part of town.

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

The bartenders at this crime-fighting theme cafe are actual private detectives by day.

D.C.'s first central library was born out of a chance encounter with the philanthropist whose name it bears.

Home of controversial poet priest who penned the words for the Austrian national anthem used in the 1930s.

Where thousands of slaves passed through the "Door of No Return."

The entire known universe of the ancient Etruscans is held inside this bronze model of a sheep’s liver.

On the outskirts of a reborn ghost town, a decaying post office remembers the bad old days.

This tiny river island switches sovereignty every six months as part of a rare, centuries-old agreement.

One of the largest helium balloons in the U.S. is a 112-foot ginormous orange.

A small marionette collection located within the dark cellars of an 11th-century Austrian castle.

This town named for the ancient God of War is home to fewer than a thousand people, but it's the birthplace of the Greek Revolution.

A medieval church built up to defend its village.