Sweden's first nuclear reactor, R1, can be visited 25 meters underground.

Elaborately carved to showcase the glorious wealth that the age of exploration brought to the Portuguese empire.

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

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

This bronze boar's snout has been rubbed to a golden sheen by visitors seeking good fortune.

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

The birthplace of Karl Marx is now a museum dedicated to the communist revolutionary's life and work.

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

The iconic boulevard is the perfect place to catch sight of a bicycling skeleton, a levitating Satan, or a chef with his head stuck in a pizza.

Turntable anonymously received orphans, alms, and groceries.

One of the most photographed buildings in a city known for its Modernista architecture is an abandoned squat.

An early 20th-century bullring converted into a modern shopping center.

Be on the lookout for the symbolic insect all over the city.

Manchester salvaged this sculpture of the adopted Mancunian when it was no longer wanted in Ukraine.

Have a seat with the father of modern computing at this Manchester monument.

A Victorian Gothic masterpiece housing a world-class collection of rare books and manuscripts.

This chimerical bridge/tunnel appears to dead end right into the sea.

A Museum of Psychiatry in a still-operating mental institution.

A wonderfully strange collection of 500+ stuffed frogs doing people things.

This former Masonic lodge has been transformed into part museum, part bar, all awesome.

Explore 400,000 years of humans' "battle against darkness" in this offbeat but thorough lamp museum.

Skyscraper powered by wind turbines attached between its towers.

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

A curious little museum dedicated to the furry feline in the cat haven that is Old Town Kotor.