Kokiri Forest (Adult):
Return to Kokiri Forest. It's now infested with monsters. Meet Saria in the Sacred Forest Meadow. She'll teach you the Saria's Song. Navigate the Lost Woods to reach the Forest Temple entrance.
Forest Temple:
This dungeon is known for its twisting corridors and ghostly enemies. Obtain the Fairy Bow. You'll need to defeat the four Poe Sisters to unlock the central elevator. The boss is Phantom Ganon. Use the Bow to shoot him as he emerges from paintings, then deflect his energy balls with your sword. After defeating him, Saria awakens as the Sage of Forest, granting you the Forest Medallion.