Near the village of Ludwikowice Kłodzkie in Silesia, Poland, there is a massive concrete decagon atop concrete pillars dozens of feet high. It was left behind by the Nazis, but no one knows what its function was.

The structure has no official name, but it is commonly known as Muchołapka, a nickname bestowed upon it by a Polish journalist. A muchołapka is a traditional Western European flytrap, a kind of glass decanter that lures insects to a watery death through a hole in its base. This name sums up the intrigue surrounding the unexplained structure.

It was most likely the the base of an unfinished water cooling tower, one of many projects abandoned around Europe by the Nazis. However, some people claim it was the launch pad for flying saucers assembled by the Nazis using alien blueprints. This casts an eerie shadow on the Muchołapka’s name. Perhaps the structure was meant to beam unsuspecting victims into the belly of a UFO, much like a fly into a trap. The decagon is situated atop Project Riese, a secret series of tunnels dug by concentration camp prisoners under the Polish countryside.

Its other equally spooky nickname given to the structure is “Hitler’s Stonehenge”, due to its blocky pillars. This association with the prehistoric monument only adds another layer of mystery to this enigmatic ruin.