Litterbox cabinet - SUCH A GOOD IDEA! Give the cats their own little litter box cubby room. It gives them their privacy and you can contain any mess on the outside of the litter box and easily clean it up.
Built In Dog House - An often underutilized area in a home is the space under a staircase. Dogs have home dreams too, and I know mine would absolutely love this! An arched doorway makes this dog den even more special.