Stacking Rainbow in Montessori, Waldorf and other homes around the world. It's open-endedness, there is no right or wrong way to play with it. 

This is about ideas of open-ended learning. That it's a puzzle in a way with an infinite number of possibilities but it does have a kind of restriction, so it's a closed system but you can approach it in all these different ways, in a multitude of ways.

-artist Emily Floyd