What was once an underground Nazi city is now Europe's largest bat reserve.

Deep in a Polish forest, this collection of Iron Age megaliths still holds onto many of its ancient secrets.

This centuries-old wooden wonder was built in less than a year and is one of Europe's largest timber-framed churches.

A haunting deserted hotel is a favorite with artists and photographers.

The silly symbol for an underground protest group is now scattered around the city.

This sprawling concrete suburb of Kraków was designed by the Soviet Union as the model proletarian city.

These massive moving sand dunes have swallowed an entire village and are still on the run.

A huge wooden clock that is so beautiful its creator was forcibly blinded.

A peculiar family mausoleum built by a German nobleman captivated by the occult.

Crosses of all shapes, sizes and colors litter the mountain, the site of a huge yearly Orthodox pilgrimage.

An abandoned Nazi explosives plant founded by the inventor of dynamite is now an underground museum.

This man-made mound monument was built out of soil from all across the Polish empire.

The unsettling remnants of a torn down movie set lies nearby the ruined location of the actual Płaszów Labor Camp.

Communism's topsy-turvy effect on Poland has been brought to life in this wacky tourist trap.

This uber-quaint Polish village is known for its habit of painting elaborate floral motifs on just about everything.

A fairytale Gothic castle steeped in Nazi treasure conspiracy theories.

The site of the first battle of World War II.

This Nazi ruin was the site where Hitler was almost blown up by a suitcase bomb.

This Polish cave has housed a dragon, a brothel, and an enduring legend.

The former Nazi concentration camp stands as a museum to remember this dark chapter in European history.

An underground city of salt.

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

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