The Building Expansion offers over 25 additional elements to expand your track vertically. You'll increase the action when increasing the height of your run with more height tiles, base plates, freefalls, switches and level. Combine with the GraviTrax Starter Set and test your skills to see how long you can keep the marbles rolling. GraviTrax is a modular, electronic-free interactive track system where you can design and build your own marble runs. This STEM toy for boys and girls 8 and up, encourages experimenting with gravity, magnetism, and kinetics to propel your marble to the finish.