Plaques on its facade commemorate the Tiber's most destructive deluges.

A rather vulgar example of the transition from Latin to the Italian vernacular.

Remnants of a 4th-century church with vivid medieval frescoes and ancient sarcophagi hide beneath this old basilica.

A detailed pachyderm supports Rome's smallest Egyptian obelisk.

One of Catholicism's four major basilicas has a series of papal portraits that are said to predict the end of the world.

Stone memorial that's said to predict the death of the pope and the site of the Cadaver Synod.

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.

The mystic whose incorrupt corpse still attracts the faithful.

Brass cobblestones mark the places where individual Holocaust victims were taken from their homes.

Installed in an act of one-upsmanship, the annual sundial in this church is also a symbolic victory for the Gregorian calendar.

A Nesting Doll of Churches.

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

2300-year-old Roman road connecting the empire.

The underground sanctuary of a mysterious ancient cult.

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

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."

This whimsical sculpture garden is a local treasure.

A house and yard adorned with bizarre concrete sculptures in a Milwaukee suburb.

Hell on Earth is actually a small town in Michigan where anyone can be mayor for a day.

Island where motor vehicles are banned -- home to the only carless highway in the United States.