Shrink and go back to the mine. Talk to Melari, who has finished to forge the sword. He gives you the White Sword! Leave from the left, go back to your size, then go down, climb down the wall until the bottom of Mt. Crenel and leave this area.
Trilby Highlands and North Hyrule Field
Cross the bridge, go east, then cross the bridge to the north and go east. Use the Cane of Pacci on the hole and switch the lever to create a bridge. Cross this bridge, go east, then north to the castle.
Get in the castle, go straight ahead, in the back room. Speak to the king, then to Potho who will tell you about a secret door. Go back down, go right (or left) and go down the stairs. Go down, left and follow the passage to the top. Go through the garden and get in the room.
Go straight ahead, then in the middle of the room, thrust your sword into the pedestal. The weapon will be infused with the first two elements. Go on one of the slabs, hold the sword button down (usually "B"), keep the button held, get on the other slab and keep holding the button down until you get the ability to clone yourself. Then, go down the stairs, stand on the second slab from the left, press B, go to the third slab still while holding B down to create a clone. Walk on the switch at the bottom, along with your clone, to open the door. Leave the castle and the garden. After a small fight and long discussions, go south until you reach the town.
Go back to the sword master to learn a new skill: the Rock Breaker. If you gathered 300 rupees, go to the shop and buy the Boomerang.