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

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

One of several skulls claiming to belong to the beheaded St. John the Baptist is on display at this Roman church.

Jesus' footprints and the first catacombs in the world.

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

The final resting place of the poets Shelley and Keats.

The skull of the patron saint of lovers lies in the Basilica di Santa Maria in Cosmedin—maybe.

The underground sanctuary of a mysterious ancient cult.

The only "Egyptian" pyramid in Europe and the legendary tomb of Remus.

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

This hidden Art Nouveau courtyard is an opulent feast for the eyes.

The yawning maw of this pagan visage is said to bite off the hands of liars.

Architectureal fantasy quarter of Rome.

Home of the first female Hungarian poet, where her secret writing lay hidden for over a century.

This eccentric folly house was designed by Romanian thinker Bogdan-Petriceicu Hasdeu, with a helping hand from his deceased daughter's spirit.

The ancient Greek Titan guards this massive dam holding a lightning bolt to symbolize electricity.

Nine centuries-old fortresses guard the walls of this medieval Romanian city.

A Romanian church built from one single oak.

This enormous abandoned prison was once dubbed the "Bastille of Romania."

Gigantic Romanian salt mines used to heal respiratory conditions.

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

No one knows who built this strange cave of worship or exactly why.

A giant portrait of an ancient king looms over the river.

Once an opulent Art Nouveau hotspot, the Constanța Casino is one of Romania's most beautiful abandoned buildings.