"Holy Wisdom" overlooks the city that became its namesake.

Yugoslavia's biggest underground airport lies in ruins.

This imposing 20th-century castle was abandoned before it was ever completed.

A tribute to the Polish insurgents who fought in the failed attempt to end their city's Nazi occupation.

The growing stones of Romania.

Check out engineering marvels of the past at this unintentionally retrofuturist museum.

Known as the Hintz House, this medieval pharmacy has been an apothecary's haven for nearly 450 years.

Once an opulent Art Nouveau hotspot, the Constanța Casino is one of Romania's most beautiful abandoned buildings.

The walls of this medieval church are covered with perfectly preserved frescos, including a pristine example of the Dance of Death.

This scale model of our solar system hid in plain sight for years before a physics team sought out all the planets.

This is not only one of the oldest collections in Europe, but also possibly the most beautiful.

A nearly 500-year-old sculpture depicts a man eating a sack of babies, and no one is sure why.

Berlin's oldest surviving academic architecture hosted decades of animal dissections.

From Iggy Pop to David Bowie to Nick Cave, this regal music studio has served some of the all time greats.

When German-Iraqi relations broke down, this embassy was vacated post haste.

An elevator into the Baltic Sea.

No need to strap in for a "ride" on this walkable roller coaster.

Berlin's old airport.

A tour of underground Berlin takes you through WWII air raid shelters and tunnels used to smuggle people out of East Germany.

Ham is serious business at the Prosciutto Museum-Serious, delicious business.

A stunning bridge that appears as if it's lunging to the shore, and has a legend of a devilish architect.

This "social palace" housing complex created a relatively stable and self-contained worker's society... for a time.

This enormous "cloth of the conquest" depicts the Norman invasion of England in mind-blowing detail.

Once the largest rope factory in Greece, this abandoned plant now stands like a ghost of industry past.