Tons of concrete used as war strategy...

Indeed. Steel reinforced cement fortifications were the very best against air and sea bombardment. I did a solo tour of the bunker complex at Fort Worden, WA. The passageways are incredibly thin, one person abreast, and incredibly long. There is no natural light either so it is entirely in the dark and you can let your imagination run wild in a place like that.

First pic is some kind of a reference or what. I mean, Im ready to go you know...