I am big fan of marble machines and similar devices which are based on the idea of perpetual motion. Metropolis II is one of such kind of machines indeed. It is a fantastic kind of marble machine and it is pretty big, too. It covers the surface of a few square meters and I have to admit that I haven’t seen such big and magnificent machine of this kind, ever before.
It features exactly 1,100 Hot Wheels toy-cars which are being constantly put on the roads. The machine is powered by engines which are used to push cars up and when they reach the highest point they are let down the roads and they reach extremely high speeds while rushing down to the bottom of the machine.
Metropolis II has been built by 12 people who have been hard working on it for more than 4 years. Project was designed by Chris Burden. [source]