Oh these are cool. When I was a teen, I stayed in one during a trek in the Alps; and then again (in another one) a few years later when I was a youth camp counselor myself. I was cooking dinner in the kitchen of the one we were staying at, and the supervisor came in, and casually told us "see that trap door you're standing on? If this bunker would actually be used during war, that's where any dead bodies would be stored in." Made for great "scary stories" around the campfire.