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

A petite castle folly in the English countryside.

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

A 200-year-old collection of oddities and medical paraphernalia.

Created hundreds of years ago, the magical follies and landscapes at this park were almost lost to time before being restored.

A rocky sea serpent hides caves, blowholes, and a spectacular natural bridge.

St. Mary's Asylum was isolated and abandoned before being converted into a Bed and Breakfast.

Fantastically decorated underground chambers built in the 1760s.

A genuine Little Shop of Horrors.

A subterranean playground in an abandoned slate mine.

This beautiful "lagoon" is actually a toxic soup filled with cars, carcasses, and trash. When warnings couldn't stop people from going for a dip, the town dyed it black.

Traveling collection of amazing automata.

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

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

A book bound in the skin of an infamous criminal, along with countless other specimens.

A 1,215-foot tunnel transports pedestrians beneath the River Thames.

Hidden behind a wall for decades, this masonic lodge was only rediscovered during renovations.

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

The John Snow Memorial marks the epicenter of London's 1854 cholera epidemic.

This foolish Victorian sea fort was converted to a deluxe hotel.

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

A collection dedicated to the treatment of disease, held in London's oldest hospital.

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

A historic house left in "dramatic still life."