A giant marble track made out of cardboard, made by a class of 17. Everyone made one part. At the end, the tracks from every student were connected, with the attempt to make one giant marble track. The most connected, working tracks in a row recorded, was four. My track was the third in the row. 

The marble enters from the top left funnel, goes down through the books, enters an elevator that starts because of the marble itself and is powered by a weight. The marble goes back up this way and keeps going by entering a new part made by another student. The tracks are made mainly individually, with matching dimensions.
In the picture with the full track, the elevator is up. If the marble were to pass it again, you would have to physically bring it down.