Take a quick field trip with your camera and visit:
* Dodge Nature Center Preschool
* Dodge Nature Center woods near the administrative offices (as a staff person to show you)
* Wargo Nature Center's "Maple Hollow"
* Maplewood Nature Center's outdoor play area
* Chanhassen Arboretum's preschool play area
I'm sure there are more examples around town, but these are the one's I know about for sure. I like Dodge's examples because they are also so clearly used in the winter, which takes up half the year in Minnesota!
In my own neighborhood, I simply cut a bunch of buckthorn trees out of the woods, de-limbed them, and left the poles stacked around. In a couple weeks, magically, lots of little "forts" started appearing around the neighborhood. Yay!