Pod Racer Walkthrough: 4: Aqualanus
This is my favorite one, the music even sounds like you're underwater at times. The fish swimming past the tunnels are neat too. The only nasty part comes about 1:20 into the lap, where the previously nice-and-smooth glass tunnels now has a jag that loves to catch you. Take it easy in that part, and the rest is smooth podding.
Another area to slow down at is the sneaky sliding doors. One side opens, the other side closes. If you ease up just a hair there, you should be able to get through the open door every time.
Pod Racer Walkthough Index