A research project done by explorers in Poland. I watched a report about this on a TV show about Poland this morning. It would be interesting to find new tunnels and see what is left of the construction. From what I saw, each time they find a new possible tunnel they can not link it back to the beginning as the tunnels were all blown up at the end of the war in an effort to keep everything secret. But, who can resist a mystery, especially one in your own backyard.

Quoted from the main page of the Sowie Mountains Research Group site:

It is 1943. The Third Reich begins to suffer heavy losses in men at the eastern front. At the same time the Allies start to bomb earth manufacturing and research centres all over Third Reich area. Adolf Hitler with his collaborators takes a decision to begin work on Wunderwaffe ( wonder weapon ). Because production of any arms in earth factories is unsafe, it has been decided to move armaments factories and research centres underground. The venue chosen is Eulegebirge ( in Polish Góry Sowie – The Sowie Mountains ). In this area wide scale geological and construction works go on from 1943 to 1945. The questions are: What for? What is to be found there? 64 years after the Second World War Sowiogórska Grupa Poszukiwawcza ( the Sowie Mountains Research Group ) – SGP is founded. The group whose aim is to explain what there is to be discovered. We are here to reveal the history and mysteries of The Sowie Mountain underground system and to show them to a wider group of people.