GraviTrax Tunnels ExpansionDetails: 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