Features: Clear instructions: comes with clear instructions so that you can start building and playing within minutes. Gravitrax: the popular stem toy for boys and girls ages 8 and up - over 6 million sold worldwide. Innovative: the gravitrax interactive track system allows you to design and build your own race tracks and experiment with gravity; magnetism; and kinetics to propel your marbles to the finish. Higher: use the height tile towers; balconies; walls and high-speed tracks to take your tracks to new heights.