What's left of the ruins of the 1893 Columbian Exhibition, or World's Fair, also known as the White City.

The small peaceful island off the Venice tourist circuit is where the city began more than 1,500 years ago.

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.

Filled with goldfish swimming in a shallow pool of sea water, this ancient crypt is more wishing well than burial site.

This private skyway is filled with art and was expanded explicitly so that Hitler could appreciate a river.

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

Jesus' footprints and the first catacombs in the world.

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

This hidden Art Nouveau courtyard is an opulent feast for the eyes.

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.