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

This ex-prison dates back to the Middle Ages.

A massive mammoth bone has been on display inside this church since the 18th century.

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

Where visitors can play more than 150 retro arcade games.

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

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

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

This mushroom-shaped rock has frustrated and fascinated locals for centuries.

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.

A somber memorial honors the hundreds of thousands of lives lost at this labor and extermination camp.

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.

This formerly-prosperous Silesian mining town was completely demolished in the late 1960s and early 1970s as an attempt to cover up a secret Soviet uranium mine.

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

In the center of Wrocław's old meat market stands a somber tribute to the city's livestock.

This Communist-era residential block is one of the longest residential building in Europe.

The coffin-shaped church was once home to monks who slept in coffins.

An abandoned football stadium with a tragic past.

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

This tower in a small Polish village uses the power of a sacred bell to ward off mischievous weather spirits.

The hollow trunk of this 650-year-old tree was used as a hideout by two Jewish brothers during World War II.

This picturesque castle in Poland has a rich history, including a legend that ties it to lost Incan treasures.

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