My next home is going to be an urban fortress aboveground with a super deep rock vault beneath it.
Insulated concrete forms solve the problem of high velocity shards flying around in an underground vault as seen in live nuclear tests by encasing the walls with a polyvinyl form. Seriously considering a really large traditional vault for my next place combined with steel drums.
I have been dreaming about this place since I first saw it ... using modern advanced construction methods for the architecture that wasn't available when it was built, like ICFs and twisted pair reinforcement for the walls and ceiling arches. I could have told these guys they were going to have damp problems with this place with a flat slab for the ceiling.