Go to Koopa Troopa Beach in the Mushroom Cup. Now, drive to the waterfall behind the beginning. Then, drive through it. You will be in a secret passage that is supposed to let you skip ahead. Drive upwards through the passage slowly and don't exit it. Drive towards the right near the non-waterfall exit. There is a small crease in the ground and if you drive correctly into it, you will sink through the ground. You will slide back if you stop, but if you drive onwards, you will fall through the ground and be picked up by Lakitu. If you're confused, use the screenshots as a guide.
Submitted by: Connie