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

In Rome’s Jewish ghetto, a 200-year-old bakery still makes the neighborhood’s historic sweets.

The burial place of an obscure North African saint was turned into a macabre body preservation factory for the 17th-century Neapolitan elite.

Water and windows define this defensive Italian well.

This beautiful park on the outskirts of Rome protects the ruins of two colossal ancient aqueducts.

This quaint Italian town keeps losing ground as the sides of its plateau slowly erode.

Skulls from the plague of 1656 and World War II bombings are united by a cult dedicated to caring for the ancient dead.

Jesus' footprints and the first catacombs in the world.

A labyrinth of ancient tunnels hidden below the city holds the ruins of 2,500 years of history.

The subterranean "lake" below the Paris opera house inspired the Phantom of the Opera's lair.

The history of radiation is on safe display at the foot of a radiation science laboratory.

A horde of stray cats rule in this secluded Parisian cemetery under a bridge.

France's most famous cemetery, with some of its most curious tombs.

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

The final resting place of the poets Shelley and Keats.

Thousands of well-dressed mummies below a monastery.

An ossuary built in 1210 to collect bones from the Ospedale Maggiore of Milan.

At the crypt of St. Mary of Eulogies and the Dead you are left alone to ponder mortality among piles of skulls.

This Romanian village may have been drowned, but it is long from forgotten.

This bone-filled cave got its name after they found 140 bear skeletons inside.

Even drowned in an ocean of toxic waste, the remnants of this Romanian village stand tall.

The legendary cliffside castle of three-time Voivode of Wallachia, Vlad the Impaler.

A small town Romanian cemetery filled with darkly humorous gravestones.

Accessible only at low tide, the deserted island is dotted with World War II ruins.