Here's a noteworthy glitch. I can barely remember it so the method may not be a guaranteed enter.
If you go to the place of the waterfall, the one where the go-kart guy is hidden, you gotta do corner glitching or anything else as long as you get on the other side of the walls, most preferably near the teleport, you gotta spam ollie in walking mode when you're walking towards the edge of the ground, if you do it right, you'll be stuck on a huge invisible floor until you respawn/change level.
Another noteworthy glitch.
If you go to the beach and find the broken rail, you can shimmy on it and get inside the ground, after that, you gotta reach the triangle-shaped floor and while walking, you keep jumping and going towards the edge. Keep at it until you reach the top.... And voila! You're on the ceiling without shameless MG, airshuffles, buttslaping, etc...