"They believed the earth was hollow and thankfully, the Third Reich wasted precious resources on expeditions to try and find a path to the interior."
Not to pick nits, but I don't believe that is true.
In fact, the closest story to this is the "expedition to Rugen" which I've never seen a source for--except crackpot "Atlantis" sites and some similarly crackpot books.
As comforting as some seem to find it, Hitler was nuts but he wasn't crazy.
I'll find you a source. Of course, I agree that this kind of foolery was not inspired by the Fuehrer himself, but by the more occult-obsessed functionaries.