This shortcut eliminates nearly the entire track! Right at the beginning, position yourself so that you are on the left side of the track, looking left. The tree should be on the left side of you, and the mountain to your right. Use a mushroom, and drive until the hill starts to go down, then jump. You should fall down into the valley, where Lakitu will tow you back up. If done correctly, you will skip a lap!
Mario Kart 64 Shortcut Video Walkthrough Series for Nintendo 64