The Mexican painter Diego Rivera created this unusual museum to display his collection of pre-Hispanic artifacts.

The industrial architecture honors the laborers who brought the Exposition Universelle of 1900 to life.

The personal library of the founder of modern neurology is open to visitors.

Architect Le Corbusier built his friend a cubist house to match his impressive collection of cubist art.

Where the high court feasted, frolicked, and high courtesans put their royal lovers' diamonds to the test.

The subterranean "lake" below the Paris opera house inspired the Phantom of the Opera's lair.

Hidden away in a modern library are the remains of one of the 18th century's most celebrated wunderkammers.

A subterranean shelter remains intact under a busy Paris railway station.

The largest medical and anatomical collection in France lies hidden from the public.

This charming cobbled backstreet is the most Instagramable street in Paris, much to the residents' annoyance.

A mechanized clock where a man fights off a dragon, crab, and rooster.

A haunting collection of the vanished and disappearing natural world.

One of the oldest medical collections in Europe focusing on rare surgical instruments.

These colonial murals are a fascinating hybrid of Spanish and Indigenous aesthetics.

This "City of Books" holds a museum, library, and the complete personal book collections of five of Mexico's greatest thinkers.

At least seven hues of blue and turquoise make this freshwater lagoon unique.

Cave where bat-eating snakes hang down from the ceiling.

A graceful natural rock formation stands astride the point where the Gulf of California meets the Pacific Ocean.

Inside this mountain lies several kilometers of breathtaking caves.

This church, buried halfway in lava rock, is all that remains of a Mexican village destroyed by a volcano.

The meteor that sealed the fate of the dinosaurs landed at this site, one of the largest impact craters in the world.

A hidden treasure of an abandoned city lies deep in the jungles of Campeche, Mexico.

The jewel of western Mexico's archaeological legacy is this tiered circular pyramid now covered in grass.

An ancient system of freshwater caves filled with animal bones, including that of species long-extinct.