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.
Petcozy is a compact geometrically shaped playground/pet bed. All you have to do is twist and attach each end to the middle. By varying the number of twists, Petcozy can become a cocoon-like enclosed space or transform into an open-top bed.