Have you heard of the Dispatchwork project? Artist Jan Vormann uses Lego bricks to repair damaged walls in cities and towns. He started in Italy but lots more places, including London, have since received the treatment.
(London, picture from http://www.dispatchwork.com)
(Amsterdam, picture from http://www.dispatchwork.com)
(Barcelona, picture from http://www.dispatchwork.com)
Makes me wish I hadn't given away all those boxes of Lego pieces after my two stopped playing with them.