This strategic isle was once swapped between empires and almost entirely destroyed in a bomb explosion.

Nearly 40 miles and 1,000 years of limestone mines under Denmark.

A natural wonder in south Denmark.

A chain of 16 wondrous lakes formed as a result of the gradual dissolution of soluble layers of bedrock.

One of the largest barracks of the Austro-Hungarian monarchy's military is now an abandoned ruin.

An industrial site turned into Hungary's most cherished natural wonder.

A floundering Polish shipyard was once the soul of the Solidarity movement that capsized communism.

This Nazi ruin was the site where Hitler was almost blown up by a suitcase bomb.

These spooky and unusual stone formations create an underworldly landscape.

The bizarre visions of H.R. Giger, tucked away in a Swiss medieval city.

Over 3km of caverns and caves at the Switzerland-France border contain the largest underground river in Central Europe.

This Irish show cave is said to have been the site of a Viking massacre that claimed 1,000 lives.

The curious and tiny collection contains some very odd objects.

The gloomy ruins that inspired Bram Stoker to bring Dracula to life.

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.

A 18th century graveyard and its astonishing cortege of macabre iconography.

360° views of the city plus five floors of optical illusions and hands-on science.

17th century streets hidden under Edinburgh were once a breeding ground for the black death.

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

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

Ruined castle with subterranean vaulted Goblin Ha' or "Goblin Hall."

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

The only fixed chain and post trail in Scotland snakes its way along the base of a towering seaside cliff.

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