The cat owners out there will probably be as impressed by this one as I was - it's an Ikea cabinet which has been converted into a cat litterbox cabinet. With a discreet 'side entrance' for the cat, when closed it just looks like a cabinet. This would be particularly great if you live in a small place and would like to have the litter tray out of sight.
The hack uses an Ikea Akrum base cabinet with two arlig doors, a pair of shelves and 4 Ikea Tryggve shelves.
The bottom third of the cabinet backboard has been cut off with a box cutter - this makes the back entry for the cat. One of the shelves sits on top of the cabinet and overhangs about 6 inches at the back - so when it's flush against the wall there's a gap for the cat to walk in at the side.
It's definitely worth looking at the article on Ikea Hacker as there are a few photos which show the nifty 'side entrance' the cat uses.
A Kickass Litterbox Cabinet [Ikea Hacker]