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

The Pope’s secret escape route.

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.

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

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.

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

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

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

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.

Two stone columns flank the grand Venice square, but there were supposed to be three.

Go inside to really appreciate this 500-year-old technological masterpiece.

Venice's "Island of the Mad."

A small island less than half a mile from Venice is a forbidden island with a dark and twisted past.

A musical instrument played by the sea.

Island wonderland for communist autocrats.

The beautiful, ornate weather station is the most popular geocache in Salzburg.

The legendary cliffside castle of three-time Voivode of Wallachia, Vlad the Impaler.

Gigantic Romanian salt mines used to heal respiratory conditions.