The walls and ceiling of this Polish church are decorated with thousands of skulls, with another 21,000 skeletons just below.

The site of the first battle of World War II.

An underground city of salt.

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

Beneath Kraków Old Town's main square lies a hologram-filled medieval market vampire graveyard wonderland.

Old cabin-like homes in a rural community untouched by time are known for their vibrant and colorful window shutters.

This wooden mosque is one of the few remnants of medieval Poland's Muslim Tatar community in this deeply Catholic country.

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

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.

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

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