The ruins of the largest gladiatorial school in Rome are largely hidden under modern streets.

An 18th century fountain and two columns are all that remains of Rome's forgotten river harbor.

This gallery commissioned by Cardinal Spada is known for its magnificent optical illusion.

A burial vault located under Tiber Island in the middle of the Italian capital.

Also known as the Square Colosseum, this building is a prime example of fascist-era rationalist architecture.

The mystic whose incorrupt corpse still attracts the faithful.

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

One of the most important yet well-hidden museums dedicated to the history of medicine.

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

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

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

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

A modern sliver of architecture in Roma.

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 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.

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

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

Inside this McDonald's you can dine on your Big Mac and fries next to a 2,500-year-old Roman wall.