One of the largest ossuaries in Spain is packed from floor to ceiling with bones.

This Arab fortress was once the largest citadel in Western Europe.

The closed and crumbling Francoist luxury resort for workers is still full of life—for now.

These ancient burial caves carved into the cliffs offer a glimpse into prehistoric funeral practices and Menorca's early inhabitants.

This grandiose staircase was part of the revival of a medieval Spanish architectural style combining Christian and Islamic influences.

An ancient stone structure that, according to legend, was built by witches.

The facade of this 16th-century building is decorated with carvings of 300 seashells.

This 19th-century fountain's namesake animal isn't what you think it is.

Giant topiary dog once played a role in a terrorist bomb plot.

Holy Grotto of Montserrat Monastery holds one of Europe's mysterious black Madonnas.

Devastated landscape used for hundreds of years by the Romans as their primary mining site.

An eerie collection of the surviving structures from a past celebration of the future.

This enchanting natural park is a magical example of a temperate rainforest in Europe.

This massive fiberglass Gulliver turns every visitor into a Lilliputian.

The world's largest wooden structure.

Natural stone arches form a walkable "cathedral" at low tide, then disappear entirely when the water returns.

Over two centuries old and counting, Madrid's massive botanical garden contains one of Europe's only desert environments.

Try not to get slimed in Tribeca.

A tour of underground Berlin takes you through WWII air raid shelters and tunnels used to smuggle people out of East Germany.

The forest hides a cemetery where members of the British Legion rest in peace.

These 17th-century mummies are no longer naturally preserved, but remain on display today.

Mummified monks and the accidentally interred, in a 17th-century crypt.

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

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