Minimalist IKEA Cabinet Hack, and lots of other ideas on hiding a litter box. Not just for the litter box but for a dog's or cat's pet bed, when company is over or just during the day, just shut the door and it won't have to be seen until bedtime.
DIY (hacked) from an Ikea basket that is bolted to a sisal scratch board as a counterweight and mounted on the wall. Add a pillow or blanket & kitty has a new perch lounge. Inspirational picture via Schwedenhacker.