This now-defunct synthetic fuel plant was once a major cog in the Nazi war machine.

The tallest stone dam in Poland was opened by Kaiser Wilhelm II himself.

For 200 years, people have flocked to this Polish town to experience the healing powers of salt.

An early creation by Erich Mendelsohn.

These beautiful castle ruins are nestled in the Polish countryside.

A Soviet era flat that refused to conform to the dull gray standards.

This dazzling wooden church was constructed as part of an elaborate peace project after the Thirty Years' War.

This abandoned but well-preserved Prussian fortress sits abandoned in a Polish forest near the German border.

The center of this Polish border town was so thoroughly wiped out in World War II that only the foundations remain.

This lakeside bunker complex in Mamerki, Poland, housed the Supreme Military Command of Nazi Germany during World War II.

One of the world's largest amber altarpieces is housed within this reconstructed medieval church.

An underground city beneath Krakow's postwar socialist utopia.

An extensive network of secret tunnels was created for the Nazi project "Riese."

A heavily politicized roundabout discussing the state of a heavily politicized country.

People in Poland have rallied to save this unnatural desert from being reclaimed by the forest.

This hilltop ruin is of the hundreds of stone columns built in tribute to the first German chancellor.

An open-air museum of 18th-century homes and churches transported from various villages in Southern Poland.

Built to transport German U-boats through the never-completed Masurian Canal, the locks near this Polish village are now home to a rope course.

Atop this library is one of the most beautiful green spaces in Warsaw.

The two abandoned overpasses are among the largest bridges in Poland.

While the U.S. and Soviet Union were engaged in a space race, Poland built a UFO on the ground.

This mysterious and once-grand memorial still embodies a remarkable architectural vision.

Dubbed "Wistom" by locals, this abandoned factory is an urban explorer's dream.

One of the largest amphitheaters in Europe is a former Nazi gathering place that still stands today.