A fairly important secret, the Waterfall of Wishing provides Link the opportunity to upgrade two of his very important items, his Shield and his Boomerang. The Waterfall of Wishing is located at the end of the river in which you get the Flippers from Zora, but on the opposite end of the river. Pass by the Witch's Hut, move the green stone to gain access to the river, and you'll be in the general vicinity. You need the Flippers to access the Waterfall of Wishing, however. Read the signs in the area to find its location, and then jump into the water. Swim north into a waterfall and you'll be in a secret cave. Now, approach the pond in the cave and it'll ask you to throw an item into the water. Throw your Shield in the water to get the Red Shield back, and your Boomerang in the water to get the Magical Boomerang back, both free of charge.