These crumbling Nazi artillery bunkers are now fair game for massive graffiti projects.

A 2017 crowdfunding campaign saved this historic castle from being destroyed.

A beautiful and classically designed villa, with an hourly infestation of monsters.

These quaint French houses dangle precariously over a precipice.

An enchanting work of outsider art, full of whimsical sculptures and carvings.

One architect's organic, human-centric design has been fully realized in this alien art house.

There's a mini version of Iguazu Falls hidden in the Balkans, and it's got a rope swing.

Dive for drinks at Croatia's first and only underwater winery.

Longest fortress system anywhere in Europe.

Notorious artist squat renovated into legal studios.

The vast, legendary catacombs hold secrets much stranger than stacked bones.

One of Europe's largest supercomputers is housed inside of a disused chapel.

Turntable anonymously received orphans, alms, and groceries.

A beautiful but toxic fountain of mercury.

This semi-secret storybook hedge maze is also the oldest garden in the city.

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.

This ancient tunnel is one of the most important examples of Roman hydraulic engineering in Spain.

This remarkable prehistoric town is full of watchtowers and houses that have withstood thousands of years.

One of the best-preserved Roman amphitheaters is still used today, but for less brutal events.

A miniature train-ride through Slovenia's largest cave system.

One of the largest caves in the world open to the public.

This massive subterranean fissure is known as the "underground Grand Canyon."

An ethereal glowing blue ocean cave in Croatia.