This is probably the most useful art installation I've ever seen. Can you think of other ones that fit this category?
Simon Maina/AFP - Getty Images
A man walks past a shack in Kibera, one of the world's largest slums, on which photographs by French photographer JR are seen on the rooftops of shacks, on February 16, 2009, near Nairobi. The photographs on the rooftops are of the eyes and faces of the women of Kibera, and most of the women have their own photos on their own rooftop. In Kibera, the material on which the photo is for the first time made of a water resistant material in an effort to protect the fragile houses in the heavy rain season as well as decorate them.