The ruins of a medieval castle linked to the murderous French lord that inspired the famous legend of Bluebeard.

Natural mummies hidden in the crypt of a medieval French church.

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

Memorial to the lost dead of Gdansk, whose resting places were destroyed during World War II.

An underground city of salt.

Real bones which are said to have belonged to a Polish dragon.

A church of bones, decorated with 40,000 human skeletons.

Two stunning 17th-century libraries and a cabinet of curiosities.

The first museum in the world devoted to sexual gadgetry.

A 400-year-old mummified arm dangles from the ceiling of St. James the Greater, serving as a warning to thieves.

A collection of anatomical samples from one of the first anthropologists to suggest that humans reached North America by crossing the Bering Strait.

Disused penal colony features prisoner artwork, some sketched in human blood.

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

This mysterious and once-grand memorial still embodies a remarkable architectural vision.