These ancient rock graves were featured on the cover of a Black Sabbath compilation album.

The largest Art Nouveau complex in the world is a Barcelona hospital with a 600-year-long history.

Bask in the 19th century grandeur of an eccentric Freemason millionaire's private gardens.

Barcelona's historic 19th-century sewers, whose foundations were laid in medieval times, are open to the public for exploring.

It’s said this crypt was the setting for the tragic finale of the Shakespeare play.

Gliwice Radio Tower, likely the tallest wooden structure in the world.

This lovely little pond is named after the hundreds of soldiers' corpses that were rolled into the waters during the French-Indian War.

A mysterious echo seems to defy the laws of acoustics.

Outside Grand Valley State University, you'll find a bench upon which many were said to have sat according to the fictional Kcymaerxthaere, waiting for a guide of time.

This solitary gravestone is separated from the rest in Appleton, explaining why local legends continue to surround it.

In the summer, the area around this sculpture transforms into a vibrant concert venue.

The final resting place of the last "gypsy king" of Poland.

This extensive collection covers thousands of years of Polish military history.

This enormous 32-foot painting depicts Poland's greatest medieval battle in glorious detail.

These 18th-century paintings of Warsaw were used to reconstruct the city after World War II.

Special benches that play Chopin's music are scattered throughout his native city.

This biographical museum honors the groundbreaking scientist at her birthplace in Warsaw.

One of the world's largest collections of medieval religious art.

A national collection of Communist-era musical posters.

The world’s narrowest house makes for an awkward, four-foot-wide living space.

A hidden art gallery in an abandoned Warsaw fort.

A program of Communist glamour in post-Stalin Poland is preserved in this colorful museum.

One of the famous Czech artist's lesser-known Prague installations appears to be a glowing fetus affixed to a drainpipe.

Tucked away in a Prague park, a statue beloved by romantics honors a poet so nice they buried him twice.