This is a sort of "crawlspace" in the 2nd basement of the science building I do research in. It's supposed to be locked, but I think that building maintenance forgot about it long, long ago. As far as I can tell, this space was created when the building was retrofitted for earthquakes a decade or so ago, and serves primarily as access to the massive ventilation system that services the labs. There are similar spaces on every floor, and a few years ago, one of the professors found someone living in one on one of the upper floors; they had festooned the walls with pages ripped from porn magazines, plastered to the concrete with what appeared to be their own feces. After that, all the crawlspace doors got locked, except for the ones in the sub-basement. I guess they figured nobody would be interested in living down here...