The odd depiction of the Virgin Mary and baby Jesus is rooted in the Catholic Church's eradication of Catharism.

"The prettiest love letters in the world" ... or so said Lord Byron.

An ossuary built in 1210 to collect bones from the Ospedale Maggiore of Milan.

A museum in the former home of Marxist revolutionary Leon Trotsky.

The famous artist couple lived and worked here, in two different houses separated by a bridge.

Diego Rivera's massive tiled fountain and failed infrastructure project.

Twelve natural mummies are displayed in the crypt of this former monastery school.

Mexico's astounding mummy museum with "the world's smallest mummy."

The largest cave shaft in the world is home to thousands of birds and popular with BASE jumpers.

A church dedicated to the Mexican skeleton saint.

High atop a Mexican rainforest mountain, this ancient pyramid once drew pilgrims countries away.

Part bookstore, part café, and part forest.

No telescopes, no power, no gift shop: The Observatory of Chichen Itza, one of the world's oldest observatories, takes astronomy back to basics.

Superstitious? Discover the witchy side of Mexico through its largest esoteric market.

Frida Kahlo's childhood home, now a museum of her life and works.

America's most famous museum of medical oddities is home to the remains of Albert Einstein's brain.

A scientific repository of goiters, boils and other ailments throughout Mexican history.

The only remaining collection of flayed figures made by French "madman" Honoré Fragonard.

This French anatomy museum greets guests with a skinless man, mid-shovel.

The world's oldest optical museum is an odd collection where the exhibits look at you.

A curious collection dedicated to human and animal anatomy and pathology.

The remains of the great moral philosopher reside in a university in London.

This small museum in a former church crypt contains artifacts of the Elephant Man, Jack the Ripper and Florence Nightingale.

One of the world's largest collections of pathological specimens.