Clutter Busting Game using ping pong balls. Each person chooses a ball, completes the task, then chooses another one. After 30 minutes, whoever has the most balls gets a prize - like a no-chores day, or gets to pick a movie, etc.
Bed frame can be changed to just about anything: constellations, gauze, mosquito net....tons of imaginary play. Walls a blank canvas to paint whatever, whenever. Maybe a chalkboard wall too.....lots of messing around like proper little unschoolers. :)