Check out the Perimeter Marble Run. The marble run set was custom built and runs around the top of a kids bedroom. It starts off with a big wheel that constantly turns and lifts marbles up. These then join other marbles which then enter a track going around the walls of a bedroom. The process sees the marbles end up at step one where they join the big turning wheel again.
The video is embedded below. For those that actually want to make one of these in their bedroom, the instructions have actually been put online and are available over here.