The ruins of an 11th-century Norman castle with a rare, perfectly circular shape.

Below a historic English market town lies a secret underground city complete with kitchens, laundries, storerooms, and an underground lake.

Pop culture has helped to keep this iconic British building from being destroyed.

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

Three bridges straddle a stream, one stacked upon the other.

A hermit's tiny cell built into the cliffside that saved him in South Pembrokeshire.

Dating back almost 400 years, the oldest public collection library in the United Kingdom was once the study hall of Karl Marx.

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

A red sandstone freestanding monolith rises out of the sea in northern Scotland.

Summer in Scotland begins with a spectacularly wild and colorful event rooted in ancient pagan traditions.

This home on a quiet suburban street is completely covered with vibrant mosaics.

A miniature Italianate fantasy village on the coast of Wales and the set of ITC classic "The Prisoner."

This well-preserved Cistercian Abbey in a romantic pastoral setting has inspired artists like the poet Wordsworth.

The bar where "The Great Train Robbery" was planned was once a nexus of high society and low morals.

A familiar otherworldly creature guards this 12th-century Scottish abbey.

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

A naturally mummified 2,000-year-old man.

Six ravens are kept captive (but well-fed) at the Tower of London to prevent the fall of the Crown.

These ancient sunken lanes were naturally tunneled into the soft ground by countless footsteps.

This Scottish bridge seems to compel dogs to leap to their death.

This legendary stone is of unknown origin, and throughout history has been a literal touchstone for British leaders.

Museum about life, death, and cannibalism in the Stone Age.

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

A clock designed to run with perfect accuracy for 10,000 years.