As the Soviet Army pushes the Nazis out of Poland, they discover a massive city of over a thousand buildings covering ten square miles that was unknown to the Allies, and using the latest science, experts reveal how Hitler was able to keep this sinister place hidden for so long. D.A.G. Fabrik Bromberg was a secret German explosives factory hidden in the Bydgoszcz Forest, providing a third of the munitions for Eastern Front.