These magnificent city walls rise from the barren sun-baked Spanish plains like something straight out of a fairytale.

One of the few remaining ancient aqueducts described by Frontinus as 'the most solemn testimony of the Empire.'

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

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

Construction of Barcelona's iconic (but controversial) church is expected to be completed in 2026—a century after the death of its architect.

One of Antoni Gaudí's most classic buildings is well-known for its "dragon-back" design.

A vista of the city and sea from atop the little-known viewing deck on an unassuming Columbus statue.

A whimsical bridge adorned with decorative dragons.

This one-time health resort was used by aristocrats around the world.

Castle and secret tunnel withstood a siege until its owner was killed by the Holy Roman Empire, while sitting on the toilet.

This Slovak bridge is known both for its connection to a national uprising and its UFO-shaped eatery.

This Slovakian statue of an emerging sewer worker might just be a bronze peeping tom.

Legacy of the earthquake that nearly wiped Lisbon off the face of the Earth.

This Industrial Age architectural and engineering gem helps visitors and residents alike traverse Lisbon, “The City of Seven Hills.”

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

An ancient and majestic fortress that played an integral role in Portugal's road to independence.

A tiny church on a man-made island in the Adriatic.

These historic defenses ensured the city within would survive hundreds of years of occupations, sieges, and invasions.

An expansive complex of subterranean tunnels is all that remains of one of Europe's most formidable medieval fortresses.

Two stone columns flank the grand Venice square, but there were supposed to be three.

Go inside to really appreciate this 500-year-old technological masterpiece.

A new sculpture calls attention to climate change in the centuries-old city it threatens.

Venice's island of the dead.

The world's oldest surviving anatomical theater, where "the dead are pleased to help the living."