I'd imagine folks could have fun doing an assignment where students create a "playground of the future" at any level. Lots of opportunities to talk about shapes, colors, math, social skills, etc.
You can read the press about Imagination Playground - they create some pretty awesome playgrounds in the here and now. I read about them in Fast Company years ago - check this design out:
The reason I thought of this article is because Wired Magazine runs a "from the future" photo contest. In the September issue someone tossed up this fun design:
Wow, there are some great ideas there. I laughed aloud when I saw the legal disclaimer and waiver kiosk - fear of litigation seems to be making so many playgrounds bland and boring.