Go to the Forest Temple. Inside, go to the second twisty hallway (with the green flying skulls) and cast Faore's Wind. Return to the red/blue switch for the first twisty hallway (the one immediately after the blue flying skulls) and hit it. Return to your warp point and backtrack to the first twisty room. Go through the door, but do not walk after he goes through the door. Turn left and walk through the hole in the wall. You will end up below the level. Turn right and you will fall for a long time and be placed back where you can do it again. Reset to get out.