At high tide this strange footbridge appears to have no purpose whatsoever.

Now famous as the "Harry Potter bridge," this impressive concrete viaduct has long been an icon in its own right.

Accessible only at low tide, the deserted island is dotted with World War II ruins.

The one-time stronghold of the noble Douglas family, now home to ghost sightings and nesting birds.

This series of Scottish caves has no clear purpose other than baffling historians.

Legend says this cave housed a 16th-century cannibal and his family of 48.

An optical Illusion once believed to be an electrical phenomenon.

This modern labyrinth lies in the shadow of a ruined medieval castle.

These ancient symbols freckling a Scottish cliff remained hidden for centuries.

A historic cave in Scotland once served as a hiding place for a famous Covenanter.

These semi-natural waterfalls hint at the park's Victorian-era industrial past.

These mysterious religious carvings were once thought to be thousands of years old but are actually the work of modern eccentric.

The mystery of this small, brick pond eluded its possibly only investigator until his death.

Monty Python fans will recognize this abandoned mine as the Cave of the Killer Rabbit of Caerbannog.

Built to hold the worst of the worst of the Nazi war prisoners.

This enchanting hill is home to fairy lore and a sinister local mystery.

This castle was established by the 4th Duke of Montrose and is connected to the Buchanan Clan.

This former Baroque palace on the historic Calle Montcada is a rare architectural gem and was once the meeting place of an aristocratic scholarly society.

Gaudí's famously flamboyant architectural style is on full display in this sprawling park and garden.

These secluded and abandoned anti-aircraft defenses have become one the most scenic viewpoints in Barcelona.

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

These ancient sea caves hold Britain's highest concentration of Pictish rock carvings.

A trio of giant megalithic stones in the middle of a golf course.

Some cheeky plantings brighten an old slipway on Scotland's Firth of Forth.