Article: For an indoor playhouse, a cardboard or Styrofoam box makes an especially easy house. You can build your own from corrugated cardboard, poster board, or any other lightweight material, but an existing box will be much sturdier. If the box is smaller than 2 x 3 feet (60 x 90 cm), you'll need multiple boxes to make the house big enough. Cats may chew the cardboard or Styrofoam, so don't use anything you want to reuse. Use a utility knife to cut through one of the cardboard boxes. Each doorway should be 6 inches (15 cm) high to fit the cat comfortably.  Cut a couple of small windows or viewing strips if you want to watch the cat while it plays inside. Glue rags or spare fabric over the doors and windows so you can give your cat some alone time. Add a couple of rooms to your cat's home with the additional boxes. To make a second story, cut a 6" (15 cm) hole in the ceiling and tape another box upside-down over it. There should be enough of a floor left for the cat to walk on. Use packing tape, duct tape, or another sturdy tape. Add a small blanket or a cat bed inside. A scratching post or rough towel gives your cat something to scratch. And of course, what cat doesn't like a cat toy? If you have a multistory cat house put an extra-fun toy on the highest level, so the cat has fun working out how to reach it. Keeping them in the house usually leads to a mess, which might even collapse the cardboard. You can move them nearby, but show your cat their new location to make sure he doesn't return to his old bathroom spot.

What is a summary?
Find several cardboard boxes. Cut a couple of doors. Tape on additional boxes. Make it cozy and fun. Keep food, water, and litter outside the house.