Plaques on its facade commemorate the Tiber's most destructive deluges.

The remains of this 2nd-century Roman temple are incorporated into a modern building.

Breathtaking and huge 430 year old maps of Italy.

Historic fortifications form the boundary of Vatican City, but it’s not entirely surrounded by walls.

Hidden beneath the famous St. Peter's Basilica is a veritable city of the dead that may hold the remains of St. Peter himself.

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

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

This small Roman arch was transformed into a dwelling by the founder of the Trinitarian Order.

Even for Egyptian royalty, the afterlife was bring-your-own-beef.

Though its celestial ceiling is impressive, the true star is the vast collection of French books.

This ancient Egyptian obelisk still bears the wounds of World War I.

One of America's founding fathers lived in this London lodging between 1757 and 1775.

These official units of measurement—including chains and perches—lie hidden beneath tourists' feet in a popular London hub.

The world's first combination ski slope and power plant.

The de facto symbol of Copenhagen is this bronze fairytale which cannot seem to keep its head for very long.

Copenhagen's celebrated theme park and gardens.

This bridge's unique architecture honors nautical heritage and encourages self-awareness.

This demon atop the Notre-Dame de Paris looks utterly bored.

The celebrated eyesore created by starry-eyed sweethearts.

The largest retailer of seashells in the world.

Electrical pylon in the shape of Disney's beloved mouse.

Some believe Ponce de León's mystical spring lurks right under a public drinking fountain.

This outdoor mural is one stop on a walking trail that weaves art and history together to tell a tale of local history.

The famous boat that once ferried Bogart and Hepburn still floats in Key Largo after being abandoned for years.