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

A hospital where antique dolls are given new life.

A Nesting Doll of Churches.

This former Roman Catholic Church still contains the embalmed hearts and organs of 22 popes.

The engineering wonder and pleasure dome of a much-maligned emperor still holds undiscovered secrets.

Virgil's many-mouthed gateway to the underworld.

A collection of objects supposedly singed by the hands of souls in purgatory.

Medieval town turned hippie commune, once home to the secret foreskin of Jesus Christ.

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

These "anatomical machines" are only one of the many strange items in this Italian crypt.

Rome's semi-secret peephole vista is also a former Crusader stronghold.

The underground sanctuary of a mysterious ancient cult.

Ruins of a 10th century church tucked away deep in a botanical garden.

The glowing blue Nymphaeum of Emperor Tiberius.

A master of trompe-l'oeil creates a stunning, tourist-fooling dome out of a flat ceiling.

Architectureal fantasy quarter of Rome.

Hundreds of lucky felines haunt the ruins where Caesar was murdered.

Stalactites and stalagmites in a beautifully lit cave.

An alchemist's "magic door" stands in the middle of a Roman park.

A submerged archeological park still holds the wonders of a Roman Sodom.

The crypts of Capuchin friars decorated with the bones of over 4,000 friars, including an entire "crypt of pelvises."

A 16th-century horror show built in a lovely Italian garden.

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

Jesus' footprints and the first catacombs in the world.