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

This abandoned Soviet circus is slowly being restored to its Communist-era glory.

This 13th century Orthodox monastery is built right into the Moldovan cliffside.

A forgotten remnant of the Soviet Union, Transnistria is an unrecognized country hidden behind a heavily militarized border between Moldova and Ukraine.

This derelict superstructure was a very important warning system for the Soviet military.

One of the most poignant ruins of the Chornobyl nuclear disaster, the local football team's stadium has been quickly reclaimed by nature.

This attraction was abandoned after the Chornobyl disaster.

The ghost town left by the worst nuclear disaster of all time is being taken over by nature and urban explorers.

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

A perfectly preserved hill village where the buildings are painted like white lace.

The blood-soaked ruins of the castle where the murderous Blood Countess was walled in alive.

The unexpectedly beloved remnants of a controversial thermal power plant.

A vista of the city and sea from atop the little-known viewing deck on an unassuming Columbus statue.

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

Abandoned waterpark turned counter-culture mecca.

Haunted tuberculosis hospital built by the patients.

This quaint Spanish village agreed to be painted blue as a marketing stunt but found that they preferred it that way.

Spanning the El Chorro gorge, this pathway used to be one of the most dangerous crossings in the world.

The world's largest wooden structure.

An eerie collection of the surviving structures from a past celebration of the future.

The oldest Roman lighthouse still in use.

These secluded and abandoned anti-aircraft defenses have become one the most scenic viewpoints in Barcelona.

Gaudí's famously flamboyant architectural style is on full display in this sprawling park and garden.

Three bridges and one giant canyon make up this fantastic Spanish settlement.