A musical instrument played by the sea.

A chain of 16 wondrous lakes formed as a result of the gradual dissolution of soluble layers of bedrock.

The remains of a sunken military ship wreck visible through clear water.

An ethereal glowing blue ocean cave in Croatia.

Celebrated example of Ottoman architecture that also served as a site for brutal massacres.

This tiny Bulgarian town offers a stunning location in the mountains and a storied history.

A Marxist summer camp full of fantastical statues lies tucked away and forgotten in the forests of Moscow.

A museum in the childhood house of a medical pioneer.

The second-deepest known cave on Earth, hidden in an extremely remote mountain region.

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

Rock carving created 1,300 years ago 75 feet off the ground.

Gigantic Romanian salt mines used to heal respiratory conditions.

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

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

This attraction was abandoned after the Chernobyl disaster.

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

The spectacular Roshen Fountain show lights up the night sky all summer long, until it "hibernates" under the ice waiting for spring to come.

Last remaining nuclear missile base in Ukraine.

The largest catacomb system in the world.

An enormous concrete structure built over a nuclear crater.

Stalactites and stalagmites in a beautifully lit cave.

Stunning Roman aqueduct used for 1900 years and still standing.

In this historic region, homes and churches are carved into ancient volcanic rock formations.

The most alien-looking place on Earth.