I'm completely blown away by the Museum of Possibilities in Montreal. It was a one-day pop-up public space project. People were invited to attach their hopes for public green space to balloons, and then others walked around and voted for their favorites with stickers.
I just love all those colorful balloons!
Check out their flickr page for some stunning photography here.
photo from http://paper.li/globalmuseum/1288898965/2011/02/03