"Shadow Play" by Richter Spielgerate

Germany-based Richter Spielgerate has recently developed "Shadow Play", an interactive playground installation in which children (I think grown-ups would like this, too!)  cast shapes and colors onto the ground plane by rotating panels attached at the top of a pole until their shadows overlap.   

Each pole provides for 360 degree rotation, and the changing arc of the sun would require some really interesting angular adjustments to get the shadows to overlap, which a group could work together to achieve.  What a great learning opportunity!

[found at colourlessdesign]