Ancient cliffs resembling a kilt on Scotland's second largest island emit an entrancing sound.

The ruins of this gorgeous clifftop castle look like something from a fantasy novel.

The hidden "ballroom" under a mansion lake was built by a criminal who ate a cyanide pill during his trial.

A 1,215-foot tunnel transports pedestrians beneath the River Thames.

The world's first underground farm is in a World War II bomb shelter beneath the streets of London.

A 168-foot tower, part of the abandoned Chester Leadworks facility.

This ancient shrine has been rebuilt every 20 years since the eighth century.

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

A labyrinth of ancient tunnels hidden below the city holds the ruins of 2,500 years of history.

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

This 700-year-old Cyprus castle is the birthplace of the world's oldest wine, said to be toasted by Richard the Lionheart at his wedding.

When a massive landslide hit one of the world's tallest dams it created a tragic environmental disaster.

This gorgeous reading room houses the oldest and largest art history library in the Netherlands.

The grassy landscape is home to the world's last truly wild horses.

A huge communist-era propaganda monument and mural that offers stunning views of the Mongolian capital.

Jurassic theme park in the small town of Erlian.

The largest dinosaurs in the world, kissing above the highway.

The unusual clock on this 18th-century market building has an extra minute hand for "Bristol time."

This narrow path was cut right into a French mountainside to feed the country's early naval expansion.

The world's tallest bridge is also possibly the most elegant.

Bordered by forest on three sides and the ocean on the other, the Great Dune of Pilat is the highest sand dune in Europe.

The medieval town's star-shaped walls are geometrically dazzling, though not entirely impenetrable.

Houses are tucked between, on, and underneath giant boulders.

Natural stone arches form a walkable "cathedral" at low tide, then disappear entirely when the water returns.