The largest free-standing aquarium in the world resides in a hotel lobby in Berlin.

This futuristic German spa allows visitors to float in a pool of salt water while zoning out to underwater techno.

A floating cat sanctuary on an Amsterdam canal.

Cat art as far as the eye can see.

This beautiful natural train tunnel is said to grant the wishes of visiting lovebirds.

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.

This sign marks the entrance to a tiny proto-state within the small country of Moldova.

The largest wine cellar in the world is a 150-mile network of underground caves near the capital of Moldova.

The romantic botanic tunnel feels like a well-kept secret.

Even drowned in an ocean of toxic waste, the remnants of this Romanian village stand tall.

A small town Romanian cemetery filled with darkly humorous gravestones.

This massive underground salt mine now holds a sci-fi theme park in its depths.

Indents in the pavement are all that remain from a grisly death machine in Paris.

The very center of Paris is surrounded by a bevy of strange good luck rituals.

A museum of carnival attractions where you are invited to ride the rides.

Notorious artist squat renovated into legal studios.

This iconic Parisian bookstore doubles as the "Tumbleweed Hotel" for traveling writers.

The oldest stone house in Paris was built by its most famous alchemist.

In the fictional world of Kcymaerxthaere, celestial wonders marked a portal to a powerful route of travel at this site in Madrid, Spain.

Abandoned for decades, trains still pass through the now-restored remains of one of Madrid's first metro stations.

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

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

Turntable anonymously received orphans, alms, and groceries.