The U.K.'s first underground railway line is now a lively thoroughfare for runners and cyclists.

These ruins witnessed the final gathering of the failed Jacobite Rebellion.

Human-made caves excavated to hide a secret society of wealthy pagans.

The oldest continual pilgrimage site in Britain was supposedly created by a gruesome beheading.

The "Bridge Over the Atlantic" lets you cross the waterway in mere seconds.

A 200-year-old prison that now houses a peculiar crime museum.

The majority of the museum's large collection is held in a storage space open to the public a few times a year.

A house of bones — but nobody is quite sure to whom they belong.

A remarkably well preserved tower dating all the way back to the Iron Age.

A museum wholly devoted to juvenescence.

The remains of a grand castle that may have inspired Bram Stoker's Dracula.

A curious collection of mechanical moving figures.

Besieged by war, this castle ruin has crumbled into a peaceful picnic spot.

Nestled amid the peaks and lochs of the Scottish Highlands, this inn and pub has played host to outlaws and ghosts.

The oldest inn in England served brew to the crusaders.

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

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

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

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

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

It is said the legendary wizard once lived in this sea cave beneath Tintagel Castle.

A site of pagan worship which still attracts people looking for fairies.

The last inhabitants of one of the U.K.'s most remote islands were evacuated in 1930.

This iconic 1,000-year-old medieval castle is a favorite of the film industry, most notably as the location for Hogwarts in Harry Potter.