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

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

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

Roman politician Herodes Atticus built this nymphaeum to honor his wife, whom he may have murdered.

This subterranean shrine beneath a bike rental store celebrates the iconic Italian scooter.

Rome's ancient Etruscan rival, now a park full of ruins.

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

A mysterious chasm in the heart of the ancient Roman Forum, the Lacus Curtius was once believed to be a gateway to hell.

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

Legend has it that any woman who kissed this statue would soon be married.

A medieval, mosaic-lined baptistry built by a heretical Christian sect.

The roof of this ancient mausoleum is made from a single Istrian stone weighing a massive 230 tons.

Psychoanalyst Carl Jung reported a paranormal experience after visiting this mosaic-lined Roman baptistry.

An incredible mosaic-lined monument said to have held the remains of an ancient Roman empress.

This 6th-century church has the largest and best-preserved collection of Byzantine mosaics outside Constantinople.

Italian poet Dante Alighieri is entombed in this small mausoleum in Ravenna, and his hometown of Florence has never been too happy about it.

Synagogue built from the stones of Solomon's temple contains the golem of Prague.

Two monstrous faces loom over a village in Czechia.

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

This mosaic-lined medieval church was built by the world's first admiral and still holds mass in ancient Greek.

Where Aleister Crowley taught magick in "La Chambre Des Cauchemars," his "Chamber of Nightmares."

A hospital where antique dolls are given new life.

This domed temple was built in a hidden cave mouth as a refuge for sinners seeking absolution.

Abandoned medieval hill town.