Your ship has minimal shields to protect you from slamming into walls as you navigate the deep underground tunnels. But it's not easy: You'll have no idea which tunnels are the fastest/shortest until a split second before you get to them, and there are alien weapons trying to destroy you along the way.

If you manage to complete the run and save the earth, you can tell the program to randomly generate an entirely new game with different tunnels for endless replayability.