I would think that one of the more important aspects of a survival bunker would be to keep it a secret. I think if it were me, I'd have it built for some other

I would think that one of the more important aspects of a survival bunker would be to keep it a secret. I think if it were me, I'd have it built for some other purpose as cover to tell the contractors involved. It could be that there are many more out there than are known, but I suppose it's a not a particularly falsifiable idea.