I spent a lot of time in here too. But you have to be careful. It gets really hot in there and humid and once I got locked in overnight as a kid and almost passed out for good because the place doesn't have a lot of oxygen in there without people coming in and out. They didn't know I was in there for hours.
They used to run model trains in there too.
Its still a fascinating place particularly in the winter when its cold outside and snowing and nice and warm inside.