This 16th-century monastery has been turned into a surrealist architecture compound.

This picturesque Umbrian city has a subterranean side that has long remained hidden.

The remains of a town so thoroughly destroyed by French forces that the citizens simply left.

This little-known relic crypt holds stolen parts of a Roman Empress.

A museum on the history of Paris, including a set of Napoleon's toiletries, Proust's room, and relics of the Revolution.

135 bronze medallions mark a French meridian line which once rivaled the hotshot Greenwich timeline.

The remaining relics of the patroness of Paris lie in a chapel under a striking double spiral staircase.

The recovered bones of martyrs slaughtered during The Terror are on display in this church crypt.

A Parisian cemetery where the elite and artistic are interred beneath an eccentric collection of tombs.

This crumbling, graffiti-covered mansion sits tantalizingly within reach of the proletariat who frequent a public park.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

The ruins of a Duke's bucolic dream, where camels once roamed alongside "Dutch" windmills and faux-Italian vineyards.

Indents in the pavement are all that remain from a grisly death machine in Paris.

Walk upon the mementos of the dead in this Parisian courtyard paved with medieval tombstones.

A lone cannonball remains lodged in the walls of the Hotel de Sens as a sober reminder of a revolution.

The oldest stone house in Paris was built by its most famous alchemist.

One of the greatest maze designer’s greatest mazes.

The final resting place of New England's last "vampire."

A small town Romanian cemetery filled with darkly humorous gravestones.

The remains of this ornate chapel now act as a portal to a cramped French cemetery.

A marvel of Byzantine engineering under the streets of Istanbul.

Idol made by King Jeroboam for the Israelites.

After this one-of-a-kind palace was built the architect's hands are said to have been cut off to keep it that way.

Once described as the "Eagle's Nest," this ruined ancient city rests on a remote mountaintop.