Instructions
Ride your innertube down the Mountain Sled Run. You are dropped into a river at the end of the run.
Paddle across the river to the entrance of the Apu Illapu Shrine. The shrine is directly across the river from where you go in the river; take care to avoid some obstacles in the water on your way over. Paddle controls are similar to the controls you use to walk on the land.
Look for the statue that has two people on top of it; a Spinja is attacking a man.
Attack the Spinja. The man gives you dynamite as a reward for saving him. You can use on the ice in the Shrine's corner, which takes you to the White Valley.