CardBoard Park
An electric vehicle filled with extra-extra-large cardboard boxes (flat of course) arrives on the site of an outdoor music festival or other outdoor event with lots of people of various ages.
The driver gets out and starts to unload sheet after sheet of flat boxes, big boxes, really big boxes, huge boxes.
Lots of Colors.
Lots of Square and Rectangle shapes.
Good, Thick Corrugate. The stuff that will hold up all day at least.
Everyone seeing the guy unload may come help, maybe not...but when he folds the first box and its big enough for a double refrigerator and says "oh, I got a small one"...everyone will get involved.
Some boxes will be 12' Long. Some will be 15' High.
Once the boxes are built - we all play. We play by stacking, we play by flipping and throwing and pushing and dominoing and learning about our bodies and experiencing space in a new way.
When the fun is over, unfold the boxes and head home - recycle the injured, burn the dead.