Those "Nazi tunnels" shown are clean, dry, and equipped with modern fluorescent lights. Those are not recently discovered tunnels. The "Nazi atomic bomb program" never went anywhere. There was one. It was never very big or very successful. The US effort to find out about the Nazi atomic bomb program was bigger than the Nazi atomic bomb program. After the war, the big-name physicists were kept in a mansion called Farm…
If anyone at Farm Hall had been working on a bomb program of any kind they would have done that basic diffusion equation calculation the very first thing, before they even started, to get an idea if the whole thing was practical. No one did. Ergo, no one was working on a bomb, or if they were they were spectacularly incompetent.