When I was little, my sister and I loved building forts in out basement. We would use anything we could find to make it into the best fortress we could. We would use couch cushions, pillows, blankets, chairs and tables. After we finished we would spend hours playing in it. We could make it into anything we wanted. We pretended it was our house somedays. Other days we would just hangout in it and read or play games. For some reason, all these activities were more fun when we were in our fort.
I had the same experience with this during the summer. The kids and I built a fort in their basement with everything we could find. Then we spent the whole day in it. We brought in flashlights, had a picnic in it, we played pretend and we played cards. They even did some of their summer reading! It was the perfect way to spend our rainy day indoors.
Image can be found here.