Once the path of a railway tunnel, now home to thousands of glowing insects.

This memorial commemorating fallen Swiss Guards of the French Revolution has been called the saddest stone in the world.

A golden plaque marks the site of the mysterious unsolved assassination of the former Swedish prime minister.

Despite the groans of archaeologists, this astounding groups of Bronze Age petroglyphs have been painted red for tourists.

This encrypted monolith protected a secret of Norse mythology by hiding in a church wall for over a millennium.

Sweden's "good old days" painstakingly re-created in a model village.

It houses the remains of a 17th-century version of the Titanic.

Stockholm's decidedly unique public transit system has doubled as the world's longest art gallery for decades.

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

A stone slab in Madrid marks the point from which the distances of Spain's national roads are measured.

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

This underground church is topped with a 500-foot cross that is seen by many as a beacon of fascist hubris.

The oldest Roman lighthouse still in use.

The final resting place of the great navigator, or maybe his brother.

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

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.

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

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

Palace where the nearly un-killable Rasputin was murdered.

A 250-year-old timepiece-automaton adorned with golden mechanical birds, which still sing to this day.

The bust of Romania’s most notorious ruler, Vlad Dracula aka "Vlad the Impaler," keeps watch over the ruins of his medieval court.

A giant portrait of an ancient king looms over the river.

Once an opulent Art Nouveau hotspot, the Constanța Casino is one of Romania's most beautiful abandoned buildings.