I've known about Cheyenne Mountain for a long time. Bored into a mountainside, not dug down into the ground, because it was easier not to move the overburden around. Whole buildings inside on shock absorbers. Even then, they realized it was a non-starter to dig downward. They also had experience installing a thousand ICBM silos and associated subsystems, including hundreds of manned control capsules. Lots of problems to solve. But this is only done when there is no other way to survive a direct nuclear hit. When that is not the object, you build things on the surface---like, for example, the Los Alamos and Lawrence Livermore nuclear weapons laboratories.

Actually, Hitler couldn't roll out of anywhere. He is dead.