This one-of-a-kind Roman arch is not actually dedicated to the god Janus.

A fortified medieval basilica on the Caelian Hill preserves extraordinary frescoes and one of Rome's most beautiful hidden cloisters.

A massive marble foot is tucked away in a small alley near the Pantheon.

The remains of the left arm of the levitating philosopher-saint are kept in a 13th-century Neapolitan basilica.

In a city that boasts four separate inclined cable railways, this is one of the busiest funicular lines in the world.

This park on the outskirts of Rome boasts two ancient Roman aqueducts and a medieval tower.

A sulfuric hellscape in southern Italy.

This is the oldest Roman-made bridge in the city still existing in its original state.

This curious, round temple is the oldest still-standing marble building in Rome.

The best preserved Paleochristian basilica in Rome hides a number of oddities and secrets.

A treasure trove of Renaissance-era funerary art in a Roman church built on top of Nero's grave.

An underground paleo-Christian burial site composed of the remains of several cemeteries and Basilicas.

This large, circular tomb is the final resting place of the first emperor of Rome.

This Roman arch marks the location of an ancient gate at one of the Seven Hills of Rome.

Dug as a secret royal escape route, the tunnel became a wartime bomb shelter and dumping ground for vintage cars.

This shining multicolored metro station deep under Naples is said to be the most beautiful in Europe.

A forgotten "city of water" underneath the famous Trevi district.

This ritzy Italian market is built around a statue of an unforgiven heretic who was burned for his belief in an endless universe.

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.

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

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

2300-year-old Roman road connecting the empire.

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