In the Big Donut level there are large blocks that are supposed to obscure your driving range. You can actually go through these. The trigger for this glitch is unknown, so it may be very difficult to do this. What you need to do is hit one of the upper corners of the block. You might need the extra speed boost only gotten from a star, or you might need to jump right before hitting the edge... but you can get in there.
Inside, there is a small pathway along the top and sides of the block. The rest is just water/lava, and falling into it causes you to lose a balloon and restart. It is a nice place to hide, though, because sometimes it's pretty hard to hit someone inside one of those things.
Submitted by: Zanto