A friend just passed this one on, and I'm loving it. The first edition happened in 2004, and it's coming back around for our viewing pleasure in 2013. The project: taking different artists' work from around the world and creating fake street signs in Lyon, France, in effect creating a huge "gallery without walls."
The round red and white signs look enough like real European traffic signs that you might take them for granted, but weird enough if you notice them to make you stop and think. This project has a delightful sense of humor, lots playful absurdity and a wonderful scale.
Take a look at the 2004 gallery.