Umm...the dungeon?
Which for me is in a room on the 2nd floor of my house; no basement (damn!) and this is out of the way and lock-upable to hide the furniture and toys (and the hard-to-explain red walls and cieling with black curtains and trim). No exposed trusses, but fairly easy to find them and install hooks.
So I guess my quirky question, which arose from the comments above -- am I odd to have a play room? Or just none posted so far? Or maybe I'm cheating...there is technically a bed in the room (although we've never slept in it); if so, I'd have to go with the stairs (some fun positions available there).