Where two rivers meet—but don’t mix.

The world's largest second-hand graces a clock surrounded by constantly changing flower beds. 

This ancient theater was once the home of fierce gladiatorial battles.

A unique underground structure dating back to the 1st century BC.

This saucy statue once caused outrage among locals.

Hilltop garden on the site of an old fortress overlooking the Mediterranean Sea.

Walk upon the mementos of the dead in this Parisian courtyard paved with medieval tombstones.

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

This former “ante-chamber to the guillotine” has been refurbished to illustrate the brutal history of French justice.

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

This 400-year-old tree is actually an immigrant from North America.

A surrealist timepiece by the artist of melting clocks.

This massive library holds what was once the largest book collection in the world.

A 16th-century fountain marks the site of a lost medieval cemetery once filled with mass graves.

A dilapidated dock tells the story of Titanic’s missed arrival.

The collection of intricate sculptures includes one carved from a mammoth's tusk

66,000 pieces of art, donated by one of the world's richest men.

One of the oldest Christian churches still standing in the Americas, and almost certainly Mexico's oldest in continuous use.

On a cornerstone of the City Museum is the head of a monstrous serpent stolen from an Aztec pyramid 400 years ago.

This clock was gifted to Mexico as a show of gratitude for its long history of welcoming Arab migrants.

Once home to an aristocratic family and a workers' organization, this intricately tiled building now houses a chain restaurant.

Gilded heaven for philatelists and architecture freaks, still in full working order despite sitting atop tremulous ground.

A jaw-dropping "megalibrary" that turns book-browsing into a geometric adventure.

In Coyoacán, a pair of coyotes crown a public fountain in reference to the ancient Aztec name of the borough.