Go inside the castle and into the room with the Link statue. Go down like you did to get the Master Sword. Down the stairs you will get to Zelda. But before she will disappear. Ganon will then laugh and sent out two Darknuts. Kill them and go back upstairs. Now head across the hall to the opposite side. These will be another electric blocker. Hit it with the sword to deactivate it. Then head on in. There will be another cursed wall that you cannot pass. Hit that with the sword. Then go passed it. Go passed the grass and go past the enemies. At the end is a hookshot target. Hook there and across some gaps. Then enter the cave ahead.

Enter ahead and into the final destination, Ganon's Tower.