A scandalous Art Nouveau collaboration that set Paris all atwitter at the turn of the century.

A surrealist timepiece by the artist of melting clocks.

France's most famous cemetery, with some of its most curious tombs.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

Dynastic Home of the De Piro Family.

An artist's mausoleum with a haunting echo.

One man's exploration of the human form, including the bizarre and delightful "Man Attacked by Babies."

The design of this beautifully crafted building was inspired by Norwegian glaciers.

One of Catholicism's four major basilicas has a series of papal portraits that are said to predict the end of the world.

This ritzy Italian market is built around a statue of an unforgiven heretic who was burned for his belief in an endless universe.

The skull of the patron saint of lovers lies in the Basilica di Santa Maria in Cosmedin—maybe.

The final resting place of the poets Shelley and Keats.

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

The only "Egyptian" pyramid in Europe and the legendary tomb of Remus.

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

Rome's semi-secret peephole vista is also a former Crusader stronghold.

The first museum in the world devoted to sexual gadgetry.

Around 100,000 bodies are buried below the medieval headstones, many of which mark graves with multiple bodies stacked up to 12 deep.

The Habsburgs' royal collections of art and wonders.

A miniature city, once ruled by the Queen of the Netherlands.

These slanted cubic abodes are a creative if odd solution to a zoning pickle.

Take a stroll through the hellish grotesques of Hieronymus Bosch in this elaborate Netherlands church.

This city square is home to Amsterdam's oldest church and a statue honoring Dutch sex workers.

The history and future of cannabis.