Spain's unique Mosque-Cathedral has been a place of worship for both Muslims and Christians throughout its history.

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

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

The other side is actually green.

A daring D-Day assault by U.S. Army Rangers is commemorated atop the high cliffs of this strategic point.

Thousands of coffin-like pillars make up this controversial Holocaust memorial.

Vienna's giant wonder wheel had a starring role in one of the greatest noir movies of all time.

Five sultans and their families rest in eternal splendor, teeming with overlooked beauty and drama.

The perfectly preserved underground rooms where Churchill plotted the war against Germany.

Giant topiary dog once played a role in a terrorist bomb plot.

Abandoned 18th century weapons factory in the Aezkoa Valley.

Abandoned Nazi train station turned underground astroparticle laboratory.

Gaudí's famously flamboyant architectural style is on full display in this sprawling park and garden.

A maze of crosses marks the jumbled divide between the Netherlands and Belgium.

This remarkably well-preserved Egyptian plinth is pretty well traveled for a giant piece of stone.

Ancient serpentine sacrifice holder that has stood the test of time.

A marvel of Byzantine engineering under the streets of Istanbul.

No one is sure if the world's fourth-largest diamond had been found in a rubbish heap or was pawned by Napoleon's mom.

The legendary luxury train passage is commemorated with a charming museum inside its former eastern terminus.

Turkish adventurer antiques in the heart of the Grand Bazaar.

A pedestrian island in the middle of world-famous Times Square emits a strange (and purposeful) humming noise.

The earliest known map to show America, discovered by accident at a Paris bookshop.

This unreal Portuguese palace looks as though it's made from a pile of different castles.

This eccentrically decorated palace is replete with grottoes, fountains, tunnels, and caves.