A labyrinth hides in plain sight at each of the city's 270 Tube stations.

This medieval sanctuary's tree-framed door looks like a portal to a mythical realm.

The heads of two giant mythological water horses honor Scotland's horselord past.

The largest greenhouse in the world is home to over one million types of plants.

A church that bred legends, and served as an inspiration for the Da Vinci Code.

The true age of this ancient stone circle is unknown, but its stunning vista isn't in question.

This massive collection of British military artifacts includes the heartbreaking personal letters of the men in the trenches of WWI.

The mysterious megaliths have enchanted and intrigued visitors for thousands of years.

A fantastic castle rumored to be the birthplace of King Arthur.

A island reachable by a causeway at low tide is possibly one of the earliest Western European locations to be identified in text.

A 2000-year-old Roman amphitheater lies just below Guildhall Yard.

Islanders once used this dramatic, otherworldly landscape to hide their cattle from Viking raiders.

This hidden green space is the city's second largest conservatory.

Northern Ireland's Brobdingnagian stepping stones.

Amazing and mysterious Neolithic settlement on Scotland's Orkney Islands.

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

"Respectful to the dead, safe and sanitary to the living, dedicated to the Genius of Memory..."

Famously misunderstood wonder of the ancient world

An ancient Scottish rock formation said to be the gravesite of a giant remains ensconced in legend and intrigue.

Catacombs turned marketplace.

The perfectly preserved underground rooms where Churchill plotted the war against Germany.

Kings Cross Station pays tribute to its role in Britain's best-selling book series.

London's creepiest cemetery was once the site of dueling magicians and mobs of stake-carrying vampire hunters.

Every Sunday, Bogotá turns 75 miles of its city streets into a bicycle superhighway.