These historic defenses ensured the city within would survive hundreds of years of occupations, sieges, and invasions.

The shell of a medieval fortress offers commanding views of the area it once protected.

Once the local rulers had gone these enchanting ruins housed common folk in an almost real life fairy tale.

An expansive complex of subterranean tunnels is all that remains of one of Europe's most formidable medieval fortresses.

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

A rotting air force base is now home to rare birds and scarce plants.

Denmark's famous pseudo-hill.

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

A nearly unconquerable island-fort in the Indian Ocean.

A castle-like sea fort from the 17th century is now a museum to oyster farming.

Fighting the British and making game shows for over 150 years.

Junkbots and mud babies are the masterpieces in this fantastically sci-fi art museum.

The premier place to experience the Victorian imagining of the steam-powered future.

For a brief time in 1960s France, families could climb into a tiny submarine and be pulled along an underwater journey.

A haunting deserted hotel is a favorite with artists and photographers.

Communism's topsy-turvy effect on Poland has been brought to life in this wacky tourist trap.

These massive moving sand dunes have swallowed an entire village and are still on the run.

The site of the first battle of World War II.

This fairytale inspired, warped building houses restaurants, shops, and a radio station.

What was once an underground Nazi city is now Europe's largest bat reserve.

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

A quarry cum sculpture park where the works of art are chiseled into the very walls.

A massive, secret marina for the Nazis' most formidable weapon in the Atlantic.

This open-air museum was originally a World War II testing ground for German missiles and rockets.