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

This huge metal monument is slowly being stripped to its concrete skeleton.

This abandoned Slovenian military barracks has become a punky-political art squat.

Piran’s oldest square is laden with history and a beautiful 18th-century reservoir.

A dead saint, a deadly poison, and a mysterious holy ooze.

The childhood family home of Italian Marxist theorist and politician Antonio Gramsci.

Venice's island of the dead.

Pilgrimage site for star-crossed lovers.

One of the most well-preserved castles in Italy also contains a rare medieval example of a port fortification.

Double spiral staircases are not unheard of, but they are very rare.

Resting in the middle of an Austrian river, this sci-fi "island" lets people cross in neon style.

Austria's ultra-modern art museum looks like Cthulhu's giant alien heart.

An Austrian house of bones filled with hundreds of intricately painted skulls.

Liechtenstein's royal family calls this medieval alpine castle home.

One hundred years ago this small house in downtown Zürich became the birthplace of the Dada movement.

Constructed along the shores of Lake Zurich, this pavilion is a walk-through work of art.

A once-thriving hotel in the Swiss Alps couldn't compete with climate change.

This demon atop the Notre-Dame de Paris looks utterly bored.

High atop the Eiffel Tower is a small apartment built exclusively to entertain the science elite and make the rest of Paris jealous.

In 1927, a biplane disappeared while attempting to complete the first non-stop transatlantic flight between Paris and New York City. This memorial stands at the last place it was seen.

These otherworldly formations were shaped over millions of years by the forces of nature.

Whitewashed mosque contains the world's largest carpet.

One of the tallest buildings in Iceland, and perhaps, the most visually impressive.

This tiny museum's sizable collection is jammed into a former underground public toilet.