Secret Shrine

The secret shrine is found in the Ikana Canyon in Majora's Mask. When you fist go into the canyon, go to the river, and turn into Zora Link. Swim to the left of the river. Once inside, you will see a door behind a waterfall. Go in that door. You will be in a large room. To enter, you need to shoot the sun above the door with a light arrow that you find in Stone Tower. When you enter the door, a man in the center of the room asks you to defeat all the anemies in the shrine. To do that, you'll need a certain number of hearst for each enemy. After you defeat all the enemies, the man will give you a Piece of Heart.