Anyway, non-fanfic, and someone said they were in the House of Leaves family of stories, so.
Dionaea House, a story told in email and chat logs. After done, go livejournal and here, and finally here.
ETA: And several other pages too found by clicking about. Huh.
I, for one, am spooked. And also, never a closet again.
For added claustrophobia, Ted's Caving Page, which actually freaks me out a lot.