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

One of the largest ochre quarries in the world, hidden in a limestone landscape.

This grand hydraulic installation has provided water for townspeople since the Middle Ages.

Founded in 670, this ancient mosque is an architectural time portal.

The other side is actually green.

The oldest known university in the world is in Fez, Morocco.

Thousands of narrow alleyways in an ancient medieval city make up what's believed to be the world's largest car-free urban zone.

Hundreds of stone stairs and a winding medieval bridge connect this haunting Spanish island to the mainland.

Over the centuries, this island paradise has done it all, from providing monks with ecclesiastical respite to sheltering an exiled Leon Trotsky.

For a brief time in 1960s France, families could climb into a tiny submarine and be pulled along an underwater journey.

Installed in an act of one-upsmanship, the annual sundial in this church is also a symbolic victory for the Gregorian calendar.

A Bronze age settlement on the Greek island of Santorini might have been the inspiration for Plato's Atlantis.

Brussels' favorite peeing boy has a sister.

The yawning maw of this pagan visage is said to bite off the hands of liars.

Hidden just under the waters around this Turkish island are the ruins of a once great city.

One of the great treasures of Neolithic art lies within this carefully constructed pile of rocks.

The mummified heart of Louis XVII, the lost dauphin of the French Revolution.

What if all public housing projects had been designed by "the Pygmalion of modern architecture," not only their prototype?

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

This salt marsh in Southern France is as pink as the flamingos that inhabit it.

Visit a surreal landscape so otherworldly NASA actually used it to train the Apollo 17 crew.

This statue was given to France by the United States to commemorate the centennial of the French Revolution.

This noble mash-up in eastern Luxembourg is part Medieval, part Renaissance, all castle.

These medieval ruins have survived since the 12th century, even providing shelter from the Nazis.