The subject of secret underground factories of the Third Reich - especially for aircraft production - is a most interesting and so far little-documented area of WWII interest.
A very interesting site which explores the factories 'Richard I-III' in Czechoslovakia can be seen at ; -
http://richard-1.com/
Yes, it's frustrating if you don't read Czech (
) but click on the links marked 'podzemi' for some intruiging photos.....
