LOL! I guess I joined the right forum!
There used to be a series on either Discovery or History Channel called “Hidden Places” that would occasionally cover bombshelters.
The most interesting one was up in the Seattle area. Self-designed by the home-owner, he built the thing under his house over the course of 15 years. By hand. Literally - he hauled out the dirt using 5-gallon buckets and all the materials he moved in were through a 3’ diameter entrance way. Thing had just about as much space as his house (standard raised ranch), over three levels. With three blast-door entrances/exits, redundant air filtration systems and multiple mantraps.
And apparently without his family having any idea what he was up to. They only learned about it (or at least the extent of what he’d built) after he died.
To say the thing was impressive is an understatement. When the show was over with I looked at my wife and said something about it being the ultimate man-cave ... and she just glared back at me and said “Don’t even THINK about it”.