A small space idea, like a tree house in your room. Utilize all space with shelf stairs up to the bed box. Get a closet too and all of it up off the floor space. Great for a boys room. Put a BB Net on the bed and voila! they can play indoors.
Diy Cardboard Slide ~When I was a kid, we did this! ***One improvement: make the cardboard about a foot narrower than the stair width, so that there is space for the kids to climb up on the stairs rather than the cardboard slide.