I wonder how much this game would cost?
Inventor Lester Clancy suggests that you get some pretending workout by hopping over the "invisible" rope that he invented, what a great invention! mind over matter especially if you are clumsy at these stuff. (Link)
I also have one, my house is like a jungle and both my kids imagine that they are the king of the forest.
See nothing on the image, use your imagination, stupid!