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

Rock-hewn monastery complex with hundreds of cave structures tucked away into the mountainside.

A Belgian self-built tower inspired by the Bible and ancient civilizations.

Beneath Kraków Old Town's main square lies a hologram-filled medieval market vampire graveyard wonderland.

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

The former Nazi concentration camp stands as a museum to remember this dark chapter in European history.

Nikola Tesla's ashes are held in a golden sphere, surrounded by his works.

An Italian crevasse filled with abandoned buildings gives visitors a look at the world without humans.

A stunning 18th-century site where pilgrims ascend by a series of punishing stairs only to return via funicular.

Local lore says the devil built this beautiful medieval bridge to help a fleeing bandit.

The dining hall that nourishes workers in Chernobyl's Exclusion Zone is also open to visitors.

One of the most poignant ruins of the Chernobyl nuclear disaster, the local football team's stadium has been quickly reclaimed by nature.

This attraction was abandoned after the Chernobyl disaster.

The ghost town left by the worst nuclear disaster of all time is being taken over by nature and urban explorers.

Clap your hands at the base of the pyramid, and the song of a sacred Mayan bird will echo through the air.

The beautiful baroque library of the Hapsburg empire.

The crypt of the imposing Stephensdom holds royal intestines and thousands of skeletons.

On the Irish coast, 18 members of the Howard family are eternally resting in an Egyptian pyramid.

The palace of the King of Kings, burned by Alexander the Great.

Named after a legendary garden called Eram in southern Arabia, built by order of Shaddad, an Arab king who wanted to compete with Paradise.

Mirrors and glass shards cover every inch of this arrestingly beautiful mosque.

A spectacular rainbow of stained glass makes the "Pink Mosque" one of the most beautiful in Iran.

A dreamy mausoleum honors Persia's most famous poet.

Light still pours into the ruins of this ancient Islamic observatory.