Some of these claims seem to be overblown.
If you take a look at the Manhattan Project, you get an idea what efforts in research and production (i.e. uranium enrichment) were required.
The Nazis never had a programm that came anywhere near these dimensions.
All they had was a handfull of phsysicists (most of the best had emmigrated to the US anyway) and a small research reactor.
So while there was some nuclear research, there never was a atomic bomb or anything close to it in Germany.
And the tunnels? The whole 3rd Reich and it's occupied territories were tunneled mostly for the purpose of weapons production.