We recently got a new dishwasher and it was delivered in a pretty big box. Of course kids can't resist playing in such a big thing. So I helped them and within a few minutes they had a full fledged private house to play in.
I cut some windows out with a utility knife for them to open and peek out or shut and be private. There are three windows, one on each side of the house.
The 4th side of the box had been cut off so the dishwasher could be removed properly. To make a door I used a piece of brown flannel I had and sewed the top into a rod pocket like a curtain. It hangs on a thick piece of cardboard that was was packed in the box with the dishwasher.
I used very little time and effort on this because I know it will not last and I may get sick of having a large box around. Eventually it will end up in the recycle bin, but for now it's getting lots of love and play time.