You guy would love my basement of my apartment. The building was built to the original owners specifications and he apparently was a retired ATF agent. It measures 9’x22’ and the thinnest wall is the ceiling which is 6”-8” (my bedroom floor) of high-pressure concrete used for high rise reinforcement. I burnt up two drill bits and gave up trying to put hooks in the ceiling. The rest of the walls are aprox 12” thick cement, block, and brick combination. It has an exhaust system and a thin (solid 1/3” thick) safe door for entry. The best thing is the new owner doesn’t even have the combo, but I took the disk lock apart and figured it out. For some reason it tends to spook people when I take them to my Recreation room. Go figure!