A national collection of Communist-era musical posters.

A mysterious structure left behind on the Polish mountainside, sometimes called "Hitler's Stonehenge".

A hidden art gallery in an abandoned Warsaw fort.

The former Nazi concentration camp stands as a museum to remember this dark chapter in European history.

This Nazi ruin was the site where Hitler was almost blown up by a suitcase bomb.

An underground city of salt.

Countless stories attempt to explain Poland's mysterious J-shaped trees.

Unique house covered in a nightmarish mural of demons, ghosts and monsters.

Enormous sandstone towers loom within a Czech forest.

The deepest sinkhole in Central Europe comes with a grisly tale and an unusual nickname: “The Stepmother Abyss.”

This former quarry is now a picturesque gorge that hides a sunken lake.

Despite attempts by local police to discourage it, Beatles-inspired graffiti has been a means for artists to air grievances for decades.

This Prague museum collects brutalist relics and memories from the country's former Soviet rule.

Walk through Czech history in Prague's largest graveyard.

A Jenga-style cylindrical tower of books that appears to go on forever.

Countless grotesque faces stare out from this eerie Prague art wall.

A steampunk-styled three-floor factory churning out art, activism, and electronic beats.

Macabre astrological automaton clock dating to the late 1400s.

A church of bones, decorated with 40,000 human skeletons.

Two stunning 17th-century libraries and a cabinet of curiosities.

The history of occult science is turned into a creepshow at this lurid Prague tourist attraction.

This outsider art house has gone from clinical creation to astounding artwork.

Each year melting snow turns these Austrian hiking trails into scuba zones.

Built to give thanks for the passing of a plague epidemic, this cathedral is a one-of-a-kind architectural hybrid.