Ten years ago we bought a house that needed some "updating".
One day as I was busy painting one of the rooms, my wife was busy pulling up the old carpet in the hall, which, at one end had a closet that wasn't but about a foot deep, just right for storing linens and such. The carpet had been installed right on into the floor area of the closet.
When she got to the closet and was trying to pull up that carpet, she came and got me because when she'd pull, the back portion of the wall would slide up. ???
After checking, I removed the shelves and some previous owner had created a false wall with the lower half, (about four feet worth), able to slide up behind the upper half, all fitted into a grooved piece of trim that was unnoticeable when the shelves were in place.
Behind that sliding portion of wall was a nice 4'x6' space that could have held all sorts of interesting things at some point. Made a great hiding place.