I have dedicated a 6' X 12' area in my room for large muscle play so that type of play is always available to the children. I change the area every two weeks so children work on all types of motor---and social---development.
Here are two examples. On the left are Stepping Stones and on the right are trampolines. The Stepping Stones accommodate many children and foster many types of group play. The trampolines do not accommodate so many children but do foster turn-taking.
A few weeks ago, a program in another part of our building received some new toy shelves that came in big boxes. Since everybody in the building knows I love boxes, they offered them to me. I gladly accepted and proceeded to set them up in the large muscle area. Over the course of three weeks, I strung five big boxes together. (There are six if you count the periscope box that allows the children to peek into box 4 and vice versa.)
I started with boxes 1, 2 and 3. I decided to orient them horizontally. I was afraid if I oriented them vertically, they would be unstable and could be prone to tipping.
For the first three boxes, only doors are on the sides and ends and only windows are on the top. I will be totally truthful: I did not do that consciously. The result, though, was fantastic. To enter the boxes, the children had to get down on their hands and knees to crawl in. That meant they were horizontal.
When the children went vertical, their heads popped out.
When I added box 4, I cut a window on the side of the box. Notice it is at the same level as the top of the horizontal boxes. This was a conscious decision because I did want the children to be able to look out of the vertical box. (I no longer needed to worry about the vertical box tipping because it was duct taped to the other boxes.)
On the inside, I connected the boxes with doorways and windows so the children could crawl and climb through and between the boxes. I taped the openings together so the boxes were all connected giving the whole structure a lot of stability.
One of the great features of the "fort" was that it provided enclosed spaces where the children could be away from the adults.