i have a clothes vault made in like the 1930s about the same size as a pop machine, built like a safe to be air tight wen locked shut. i was always gonna get to finishing the inside like that but never had the time. should probably just sell it to someone handy who can be creative with it and get some use out of it.
I've seen an industrial sized electrical cabinet used as a "safe". The guy bought it at salvage from an old factory. He had it in his garage with empty conduit lines running up into the ceiling, and the "warning; high voltage " placards on the front of it.