Revised new edition 2011. In this book, Jochen Bergmann shares his personal experiences, dating back to his youth, of exploring old mines and U-boat relocations from World War II in the Porta Westfalica area. During this unique pastime, the author encountered not only fascinating remnants from a time that subsequent generations can hardly imagine but also many individuals with whom he shared this special hobby. The author investigates, among other things, whether the facilities he visited were solely used for bomb-protected production or if highly classified research was also conducted there. What are the reasons that some entrances to certain facilities have remained open for decades, while others were sealed off with great effort, sometimes even involving helicopters?.