Huge concrete structures designed as an early warning system for Britain to detect enemy aircraft.

An engineering error ensured this cavernous 350-foot-long subterranean thoroughfare was never used as intended.

This tiny island featuring 9th-century Viking ruins is only accessible at low tide.

Cliffs full of fossils at the portal to England's Jurassic Coast.

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

A village on the east coast of England that has almost completely eroded into the North Sea.

Colin Stokes "got a bit carried away" and built a castle that looks like something out of Tolkien.

This tiny little cave was said to have been a refuge for a saint with a glowing arm.

This allegedly haunted 16th-century tower house-turned-museum exhibits thousands of spectacular objects.

Overlooked by many, the two famous Scottish warriors guard the main gate of Edinburgh Castle.

High Victorian fantasy created a fairytale castle out of a ruined fortress in Wales.

A fernery hidden by neglect is uncovered, and an ancient specimen along with it.

A meandering boardwalk across the bogland leads to a "stairway to heaven" with sublime views.

This lovely little burbling creek is actually a deadly waterway that has dragged down everyone who ever set foot in it.

The largest oak in England is said to have been the hideout of Robin Hood and his Merry Men.

This hospital once pioneered the use of electroencephalograms, but fell into maltreatment, abuse, and eventual abandonment.

No one knows who created the statues or if they are arranged properly—let alone the artwork's real name.

The Stonehenge of Wales is one of the grandest neolithic dolmens still in existence.

Eyam took steps to quarantine themselves and keep the plague from spreading.

A Roman spa buried deep beneath the City of London.

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

The ghosts of Britain's telecommunication past sit rusting away in a small village in England.

This ethereal, rainforest-like gorge is home to waterfalls, quaint bridges, and fairy folk.

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