The water-powered carriages are long gone, but for over a century this funicular railway has been the fastest route to the highest point in Paris.

This historic island prison holds one of the dungeons from the Count of Monte Cristo even though it is a work of fiction.

A cave dwelling that was started by the Celts, expanded by monks, and finished by knights.

This whimsical castle of grottoes was the labor of love of a French postman, and one of the greatest achievements of outsider architecture.

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

Amsterdam's Red Light District leaves little to the imagination.

The former home of a mad diplomat is said to still be marked in bloody, arcane scrawls.

A unique collection of gilded age mechanical pianos.

Seven mini rowhouses fill the gap between 54 and 70 Westerstraat.

An ancient passage filled with stalls selling used books, once frequented by Vincent Van Gogh.

This gorgeous reading room houses the oldest and largest art history library in the Netherlands.

Ancient paintings known as the "Sistine Chapel of Cave Art."

Medieval museum built over Roman baths that features famous tapestries of a lady and a unicorn.

An "inside out" building in the historical center of Paris, featuring Europe’s largest modern art museum.

This iconic Parisian bookstore doubles as the "Tumbleweed Hotel" for traveling writers.

The oldest stone house in Paris was built by its most famous alchemist.

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