Charles Dickens was not a fan of the ghastly wall dressings in this 6th century church.

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

Gods clash with machines in a power plant regenerated as a museum.

The "Greatest Sewer" of ancient Rome is one of the oldest sewer systems in the world, and is still in use.

More sculpture than building, this architecturally significant temple was built on the spot of Saint Peter's crucifixion.

The martyr's wax-enhanced skeletal remains lie preserved in a glass case in the Santa Maria della Vittoria in Rome.

This ancient Roman prison is decorated with an upside-down cross not as blasphemy but as saintly tribute.

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

A Nesting Doll of Churches.

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

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

Jesus' footprints and the first catacombs in the world.

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

Architectural monsters are devouring this palace's every door and window.

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

The final resting place of the poets Shelley and Keats.

2300-year-old Roman road connecting the empire.

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

The underground sanctuary of a mysterious ancient cult.

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

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

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

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

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