An Escher-inspired library dedicated to the wonders of the human mind, yet closed to the public.

An abandoned set from the 1980 film "Popeye," claimed and repurposed as a theme park by creative locals.

Eccentric concrete mansion and museum designed and built by hand from the inside out.

An eccentric inventor's castle home with its own indoor weather system.

This woodland architectural installation acts as a camera obscura for the heavens.

The most iconic structure in Scotland has been home to bishops, colonels, and Sean Connery characters.

One of the oldest reform schools in the United States, home to wayward boys such as Merle Haggard, now abandoned.

Winding paths and ramshackle mausoleums in the oldest "park cemetery" in London.

Europe's second largest ossuary wasn't discovered until 2001.

A science teacher's dream.

Skeletons dressed in extravagant 18th century royal costumes cavort in the aisles of this German basilica.

Trails through lava-carved tube-caves display sparkling bacteria and a rich history.

A 19th century artistocrat's mansion, turned into a library, hidden in a modern library.

Shop of curiosities with a dinosaur museum tucked in its basement.

A dilapidated dock tells the story of Titanic's missed arrival.

The walls and ceiling of this Polish church are decorated with thousands of skulls, with another 21,000 skeletons just below.

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

An encyclopedic collection of mammal penises.

On the top floor of an upscale department store stands a lavish restaurant housed in a replica of a luxury French dining car.

A haunting collection of the vanished and disappearing natural world.

The last moments of the ill-fated Pompeiians, frozen forever in plaster.

A self-built castle made by a mysterious man.

Popular tourist destination where witches in dark hats sell dried llama fetuses for good luck.

The most visited, and possibly most controversial, museum in Germany.