Secret Training Course:

Go to track 6. Right when you start turn around and
soon you will see a big hill. drive up the hill and
follew the road. You will see an intersection but 
keep going straight. soon you will see a danger sign
over a dirt road. go on the road and stop right 
before the checkpoint.Go off the cliff to your left
but dont touch the water.turn right and drive along
the water. If done Right, you'll see a Tunnel in the
Ground!