The interactive ball track system from Ravensburger. With the GraviTrax marble run system, you can build your own marble run world by creatively using the laws of gravity. Use the various building elements to create an action-packed course and use magnetism, kinetics, and gravity to get the marbles to the finish line With the GraviTrax marble track system, you can guess gravity in a playful way, and with various expansions, it can be enlarged for unlimited building and playing fun! Add even more speed with the expansion sets.