A marvel of Byzantine engineering under the streets of Istanbul.

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

The most elaborate of 12 medieval arched doorways to the old city of Burgos.

A fountain standing as a testament to a doomed alliance.

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

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

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

The ornate miniature mansions were built for Istanbul's feathered residents.

This private skyway is filled with art and was expanded explicitly so that Hitler could appreciate a river.

A historic castle that served as a backdrop to part of an elaborate extraterrestrial hoax.

Whimsical sculptures and caves chiseled by nature over the millennia.

Long tunnels run under the ancient chariot racing circuit to the tower.

Rare wooden escalators lead deep down into an otherwise staggeringly monotonous tiled tunnel.

Touching this little fossil embedded in the wall of a grand mosque-cathedral may make your wishes come true.

A curious carving hides on a marble column in the Mosque-Cathedral of Córdoba.

This 19th-century fountain's namesake animal isn't what you think it is.

This innovative steam machine was no doubt the most famous of the pioneer locomotives.

This whimsical statue dumps water on its head to symbolize knowledge flowing into his brain. Or maybe booze.

A medieval military street hidden beneath a charming French fishing village.

Originally used to sell brandy, the bull-shaped billboard became an iconic symbol of Spain.

A tilted half-timbered house from 1672 is built into a salvaged segment of a medieval wall.

This beautifully verdant lagoon is tucked below a massive volcano in a crater atop a black pebble beach.

This spectacular dome managed to survive after being bombed in World War II, in an event known as the "Miracle of Mosta."

The small alleys in Lübeck's Old Town are a result of medieval urban sprawl.