Sleeping nook with reclaimed windows as doors. I deeply love this - I've always found the cubby/fort/hideout space very comforting. I like bunk beds, the bottom bunk, because they give one a sense of that. Though as a 6'3" adult, sleeping in the bottom bunk is not all that doable. Twice I've lived with my bed in a closet - this is just a much classier version of that.
i LOVE this. The bed looks so cozy surrounded on three sides like that and you have room for so many books at your immediate disposal! :0) Then, of course the storage room is awesome. This is just so efficient, it makes me slap-happy.