First, find the owl in the Mountain area with Goron Shrine, then after he talks, he'll fly over a huge hole and leave feathers on invisible platforms. Cross them to find the Lens of Truth. Then go back across and use the Lens of Truth to find Darmai's ghost. Talk to it, then follow it. Then when he goes up a cliff, use the lens of truth to find a ladder in it. Go up the ladder and sometimes it will have a fork in the path, go right, left, right in this order whenever you come to at least 2 ways. When you reach the top, follow Darmai into the grave place then talk to him and when you regain control of yourself, play the Song of Healing to find the Goron mask.