This is my personal favorite mini-game of all, but before being able to play this game, you must first have finished the Temple of Ice. Upon completion, travel to the Southeastern area of the sea chart and sail as far south as you can until you find a cluster of rocks. Edge slightly East of the rocks to find an island shaped like a DS. This is aptly named Dee Ess Island. Dock your ship and talk to the Goron who will allow you to play the Goron Racing game. You will be charged a small fee of 50 rupees, but like the other games, the rewards are worth it.
During this game, you will play as GonGoron only. Rolling through the course and breaking as many Blue gems as possible is the way forward to victory. Keep your eyes out for the Rupees also though, as you can never have enough of these. The map is your friend here and it will pinpoint the locations of the Blue gems, while the left side of the screen will show you how many you have left to break. To get a speed boost, simply roll over the arrows on the track. This will enable you to break the gems faster, however, control yourself, or you may find that your missing more gems than you can afford to. Once you have broken all the Blue gems, a door will drop down to reveal the exit.
Simple really, and quite fun to boot. Below are the rewards for all of your hard work.
45+ seconds = Blue or Red Rupee
45-36 seconds = Blue, Red, Big Green Rupee
35 seconds or less = Big Red Rupee, Treasure, Bombchu Bag or Ship Part.
Note that the Bombchu bag and the Ship Part are only obtainable once.