After your meeting with Zant, who took the Fused Shadow from Midna and tried to put Hyrule into twilight again, you will turn back into your wolf form with Midna in a pretty bad shape. The Spirit Light Laynaru suggests you should go to Princess Zelda in Hyrule Castle. In the field, go east, then south and enter the Castle Town.
Hyrule Castle Town
Go to the southern street, then to Telma's Bar and try to get in. Upon leaving, Louise, Telma's cat, will recognize you and will show you the way. Push the isolated crate towards the window, jump on it, then on the others and get in. Go ahead on the ropes to go across the room. On the third one, you can listen to the guards' discussion.
In the next house, speak to the man, then use your senses and attack the spirit with your Ending Blow to defeat it. You will receive a Poe's Soul! Speak again with the man, Jovani, who asks you to find 20 Poes so that he can get his soul back, then he will open a passage to the underground waterway of the castle. Get into the chest.
Go north and grab the handle to open the door. Climb on the stairs and attack the Skulltulas on their sides or in their back. Pick up a stick, put it on fire and burn down the web. Go ahead, get rid of the Keeses, then pick up another stick. Go light it up in the previous room, then come back and burn down the web to the west. Go ahead, attack the Keeses and the Bokoblin, then the next one in the next room. Use your senses and dig in the centre.
Go ahead, climb the stairs, go across using the rope and climb this way until you reach the top while fighting enemies. Then go through the door. Walk on the roofs, climb on the crate, jump to the other side and go on northwards. In front of the hole, go ahead on the floating bridge as soon as the wind is starting to blow. Then jump on to the blue roof on the right, go to the top of this roof, avoid the bird and get inside the tower. Climb the stairs and get through the door. You find back the princess. As she's curing Midna, Zelda will advise you to go to the Sacred Grove to find the blade of evil's bane and get back your human form.
Outside the castle, warp to Northen Faron Woods, and head north. Get rid of the puppets and the monkey will show you the way to a nice wooded area on the other side of the cliff. Look east and climb on the platform, then with Midna's Help, jump several times towards the new path to the east. Get on the footbridges when the wind isn't blowing, then cross the gap using the ropes. Listen to the Howling Stone whistle a bit further. Repeat it twice and a wolf mark will appear on the map. Next, get in the passage.
Once you have reached this new place, look for a stele on the left, listen to its whistle and repeat it. A "skull kid" with a blue lantern will appear and cast puppets to help him. You will now have to find him and attack him from above. From time to time, get rid of the puppets using the jumping attack, but they will constantly respawn (don't use Midna's circle attack, it's too risky). From this area (the entrance is locked - indicated by two torches), follow the underground passage, then right after it, go right. Afterward, go straight ahead, climb on the ledge and attack the Skull Kid.
Come back, go across the water and get in the new tunnel between the two waterfalls. From there, go right and follow the tunnel. Now you are in an area with a huge waterfall and deep water. Get rid of the puppets, then quickly go across the water, go under the waterfall and climb to attack Skull Kid.
Jump further, follow the tunnel on the left and you are again in the area where you found him for the first time. Follow the right path towards the next area, then go straight ahead across the shallow water and take the tunnel going in an upwards slope. There you are in an area with a big sealed door and Skull Kid is hanging on a branch far above you. Follow the tunnel on the right side of the door, then climb the stairs in front of you, follow the path leading to Skull Kid and attack him.
Then jump all the way down and take the passageway to the right that is now accessible. Go straight ahead, then follow the left path and jump down in this new area. Here the Skull Kid will jump from stump to stump. Get rid of the puppets, then quickly jump towards him and attack him. Do this twice more and he will finally vanish! Follow the new passageway.
Stand on the Triforce symbol and howl the melody. Now here is a complex puzzle where you must put the two guardians back on their original slab. The rules are easy to understand after a few tries. There are several solutions (both working for the Wii U, Wii and GameCube), here is one: down, up, left, up, right, down, down, down, up, up, left, up, up, right, down. Next, go straight ahead and check the sword, the well-called Master Sword!