The Korok Forest is a location in The Legend of Zelda: Breath of the Wild. It is the home of the Koroks located in the region of Great Hyrule Forest. The Master Sword can be found here guarding by The Great Deku Tree.
In a small hollowed out room inside The Great Deku Tree, Link can find a Mushroom Shop called Spore Store, the General Shoppe which functions as Korok Forest's General Store, and an inn inside the Great Deku Tree's Navel. According to Natie, this hollowed out room is actually The Great Deku Tree's stomach, and a cooking pot is found in the middle of the room.
Link can also climb the Great Deku Tree where he can find Walton who gives him the side quest "Riddles of Hyrule". Fairies can also occasionally appear on top of The Great Deku Tree near Walton as well.
Master Sword pedestal
After removing the Master Sword from its pedestal, Link receives a vision showing Princess Zelda brought the Master Sword to the forest for safekeeping and spoke with the Great Deku Tree, after Link was sealed within the Shrine of Resurrection during the Great Calamity events. Zelda reveals to him that she heard the Spirit of Master Sword telling that her destiny was not finished. Zelda then places the Master Sword in its pedestal and leaves to seal Calamity Ganon in Hyrule Castle.