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.
A good idea for a small bathroom, under hanging shelves for things like cotton balls, cotton swabs, etc. Also great in the kitchen, for a spice rack over the stove. Just hang jars from bottom of the cabinet.