One screen down from the Tokkey hut is a cave at the corner of the cliff. Enter it and use the Long Hook in order to reach a chest containing this ring at the left side of the cave.
Fairies' Woods - Present
Located in the east-most part of the woods is a chest surrounded by pits. Jump over the pits to obtain the ring in the chest.
Nuun Highlands - Present
On your map it is the screen to the left of the Maku Tree. A chest can be found inside the cave.
Sea of Storms - Past
One screen up from the land mass. It is marked above the sea by a mass of rocks. Use the Mermaid's Suit to dive under the water and enter into a cave where you will find a chest.
