Secret passageway! Cute idea if your house is designed properly. I remember a family friend's house had a hidden play room under their stairs. To get in, we crawled through a little door in their coat closet. Way fun for kids!
I want like 30 different places like this in my house oneday! Could you imagine how fun adult hide in seek would be?!?! Attic Hidden Door by Eudaemonius, via Flickr
secret bookshelf door. I used to have a door like this at my apartment at sixteenth and Granville in Vancouver ! It had was a door to a closet that was the full tenth of the room and came out in the next room!