I'm just guessing out loud here, Gordon - so don't assume for a moment that I know what I'm talking about....
I haven't seen anything exactly like it, but the brick ( not concrete ) construction, with no windows but reasonable ventilation, plus earth-wiring....
Could it be a large pyrotechnic, or ammunition, store of some kind ? This could possibly be an explanation for the 'zig-zag' baffle - to break any blast from inside as well as out ?
