Large, airy hallways hide within an impenetrable fortress that beckons urban explorers.

A forgotten monument to Yugoslavian freedom.

A Brutalist monument in the middle of a housing estate by artist Victor Pasmore.

This Roman archeological site is hidden amid a 1930s housing estate.

This sculpture commemorates a naturalist and an illustrator whose work was a forerunner to modern field guides.

This century-old grotesque has a mysterious history and may not actually be a rabbit.

One of the largest wooden constructions in Europe was meant to be a casino, but soon became an orphanage.

Over the centuries, this island paradise has done it all, from providing monks with ecclesiastical respite to sheltering an exiled Leon Trotsky.

The only residents of this abandoned housing development full of identical castles are stray cats and dogs.

It's hard to believe the dizzying patterns covering this abandoned mine are completely natural.

Moscow's other, lesser known kremlin is a fairytale-like cultural complex modeled after Old Russia.

This ancient village and its adjoining cemetery have a beautiful history of death and remembrance.

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

This abandoned limestone quarry now provides visitors with multiple, breathtaking viewpoints.

Harry Potter’s Hogsmeade Station is also a charming blast from the past situated in North Yorkshire.

Abandoned for over 20 years, this Art Deco seaside swimming pool is a magnificent waste.

At 22 feet tall, these Bronze Age monoliths are some of the tallest standing stones in the United Kingdom.

The remains of a remote village that once housed over 1,200 dam workers and their families.

A series of idealized caves carved to entertain guests.

For decades, a bottle factory dumped their waste into these waters—now it's considered the best sea glass beach in England.

Home to the longest wooden escalators in the world.

A labyrinthine network of chambers with a storied past hides below Edinburgh's South Bridge.

This castle resides in a valley known for immense bloodshed during the Middle Ages.

Twice a day this ancient path disappears with the tides, leaving the Holy Island of Lindisfarne out to sea.