The Tunnels Expansion Set adds stealth and surprise with 18 all-new elements. Use the straight, curved and vertical tunnels to hide your marbles as they fly through your tracks. Test the new Bernoulli and o-tracks to see how much speed you can generate and where you can drop the marble to a level below. Combine with the GraviTrax Starter Set and experiment with different elements 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.