The tradition of open-air secondhand and antiquarian bookselling in Paris dates back to the Renaissance.

This massive blockhead sculpture hides an entire library.

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

A detailed pachyderm supports Rome's smallest Egyptian obelisk.

A wunderkammer of curious objects and intriguing art nestled within a hub of ancient Roman sites.

The best preserved Paleochristian basilica in Rome hides a number of oddities and secrets.

Brass cobblestones mark the places where individual Holocaust victims were taken from their homes.

The engineering wonder and pleasure dome of a much-maligned emperor still holds undiscovered secrets.

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

Rome’s legendary peephole vista is also a former Crusader stronghold.

An imperial church bombed to ruins during WWII now stands as a jagged memorial.

Cold war icon and onetime "hole" in the iron curtain.

Thousands of coffin-like pillars make up this controversial Holocaust memorial.

The largest free-standing aquarium in the world resides in a hotel lobby in Berlin.

The most visited, and possibly most controversial, museum in Germany.

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

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

An eccentric Victorian aristocrat's enormous collection of medieval armor and weapons from around the world.

This pub boasts a curious history and may have inspired a Dickens character.

The ruins of a church destroyed by both the Great Fire of London and the Blitz, now turned into a peaceful garden.

The Great Fire of London and the regulation of one-way streets both started in this alley.

A mysterious shape catches the eye in this 16th-century painting.

Legend says these colorful, invasive residents are the descendants of birds released by Jimi Hendrix.

This bewitching Babylonian goddess haunts a hallway of the British Museum.