First, select the snow stage. (I would recommend using the Military Vehicle) From the starting point, just keep moving forward. Go straight through the frozen pond and under two bridges on the left side. Now, exit the lake on your right so that you don't fall off the waterfall. You should see a dirt road. Follow it until you see another lake. Take it. After the lake widens on your map, take a sharp right. You should see a big mountain, so drive over it. You should be pretty high. Now, drive straight off the cliff when you see a road coming from a tunnel. There should be an indent between the two hills, so go through it. Keep following the indent and over some train tracks. As I said, keep moving forward! When you see the road in front of the mountain barrier, take it and go to the right. Here, pause the game and type in the Light Cars and No Gravity cheats located on this page and then follow the road until you see some deer. The deer show that the dirt road will show up on the left, so when you come across it, take it. The trail will swerve right, so take that. If you see more deer, you've gone too far. When the trail turns left, climb up the hill on your right. Now, accelerate down the hill, giving you enough velocity to fly over the mountain barrier. Now when you are atop, you may discover an invisible wall. (Depending where you are). Look for a hill going downward into the other end of the world, the invisible wall. Drive down it, and you should enter the abyss! As you are falling, you will get to a top speed of 1,118 miles per hour!
PS - You can enter the Faster Time cheat so that when you spin in the air you will go crazy fast! You may also experience what I like to call the 'Shadow Car'!
Pause the game and press R1,L1,L1,R2,L1,L1,L2.
Pause the game then press R1,L1,L2,R2,Right,Right,Right.
Pause the game and enter the following code:
Press R1, R2, R1, R2, Up, Up, Up