It was hosted by a club at my college, in the campus' big math and science building. It's a pretty big building, with a hexagonal core (the photo is taken in a lecture hall in the basement of the central Science building) and two wings branching off of the core, North Hall (with lots of math classrooms and science displays) and DeVries Hall, with a big multi-level atrium and most of the bio and chem labs. Naturally, we weren't allowed in any rooms, but we still had free rein over all four floors of the entire complex.
The different parts of the building allowed for all sorts of different strategies and playstyles, because of the different floor layouts and architecture - North Hall is pretty much a straight line with a small loop at one end and staircases throughout; but the lights in North Hall were intentionally left off, allowing for all kinds of ambushes in the dark alcoves for classroom doors or study areas.
The Science Building has a hexagonal floor plan, with additional side routes and hallways to provide access to all the classrooms, staircases, etc. This made it great for flanking or running away, because you could just run around until you managed to loop behind your pursuer, or you could change floors using one of the many staircases.
DeVries Hall is designed to be more of an open space than the utilitarian Science Building, which also means that there are lots of places to move large groups through, which is a problem in the narrow staircases and halls of the other two areas. You can also stand on the third floor balcony and shoot someone who is standing in the basement, which is pretty funny.