This may have hit your radar already, but it's such an amazing accomplishment I have got to post it here. Behold Scott Weaver's recreation of San Francisco. This huge 3 dimensional model is also a ping-pong ball run. It was made over the course of 35 years with...get this...over 100,000 toothpicks! The balls can start in several different spots, each of which will send it on a tour of a particular section of the Bay Area.
[ Thanks Tom! ]