An 18th-century post box used to alert the church of sick and ailing foreign pilgrims.

A master of trompe-l'oeil creates a stunning, tourist-fooling dome out of a flat ceiling.

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

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

This hidden alley near the location of Rome's first theater was the site of a curious miracle.

This small church was constructed over the ruins of three temples dating to the Roman Republic.

A 15th-century monumental Latin inscription on this house celebrates Lorenzo Manilio's love for Rome.

This is the oldest Roman-made bridge in the city still existing in its original state.

A rare example of a medieval house in Rome adorned with a melancholic inscription.

This small, ancient Roman temple was once a church dedicated to the patron saint of penitents.

This curious, round temple is the oldest still-standing marble building in Rome.

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

An ancient Roman temple first dedicated to an emperor's wife is now a church.

A monumental fountain in Rome features a large statue of Moses that has been criticized for centuries.

An ancient Egyptian obelisk is now used to commemorate fallen Italian soldiers.

A sculpture serving as an homage to Pope John Paul II.

A Parisian cemetery where the elite and artistic are interred beneath an eccentric collection of tombs.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

If you look closely at the oldest bridge in Paris, you might notice hundreds of ugly faces leering from its sides.

The approximate spot where the last Grand Master of the Knights Templar was put to death.

The oldest continuously operating mint in the world that has been making coins since the 9th-century.

A beautiful Victorian statue shows France's enduring love of the rhinoceros.

This bridge was constructed from the rubble of the infamous Bastille.

This life-size replica of the Statue of Liberty's flame is also a tribute to Princess Diana by default.