After you help resolve the regional phenomena, Princess Zelda is seen at Hyrule Castle beside a red moon. You must go to the castle to look for Zelda.
Complete Regional Phenomena and talk to Purah
Before you enter Hyrule Castle, you might want to complete the four Regional Phenomena quests:
- Hebra Regional Phenomena
- Eldin Regional Phenomena
- Lanayru Regional Phenomena
- Gerudo Regional Phenomena
After you complete all four, go to Lookout Landing and go to the roof of Purah's lab, and talk to Purah. There will be a cutscene.
How to Enter Hyrule Castle
You can reach Hyrule Castle by launching yourself with the Lookout Landing Skyview Tower, then glide north. You may need extra stamina to get there.
Go to the Voice
When you land on Hyrule Castle, a voice will call to you. The location will be marked on your map. Before you go, you can go to Serutabomac Shrine, which is northeast of the Sanctum.
Then go to the destination in the southeast part of the castle. This is the Second Gatehouse. Glide down to find Zelda. She will disappear, and you must battle monster forces consisting of Black Bokoblins and Black Boss Bokoblin.
Go to the Second Destination
The next destination is to the north. You can reach it by going to Serutabomac Shrine, then go down off of the southwest edge of the ledge and turn east to see stairs leading down. Go down these stairs and you reach the Library.
Go straight down, then turn around and use Ultrahand to move the bookshelf out of the way. You find a shield and the Royal Guard Boots.
Approach Zelda and you will fight more monster forces, consisting of Chuchus and a Hinox.
Go to the Third Destination
Go north to find Zelda again. This time, you must fight Gibdos.
Go to the Fourth Destination
To reach the next destination from here, go north and up the stairs, then make your way southwest. Defeat the Horriblins in the hallway, then continue going southwest. You can see a tower to the south. Make your way to that tower, defeating any enemies that get in your way. The destination is on B1, so use Ascend as needed. If you go too high, there is a hole in the floor of the tower that you can use to fall into Zelda's room. Approach Zelda and you will battle three Fire Lizalfos.
Go to the Fifth Destination
Go up one floor, then go west across the bridge, but beware: the middle of the bridge will fall. The room on the other side of the bridge contains several strong weapons.
Go out of the tower and glide down from it to the west side of B3, where there is a door in the wall. It leads to the next destination, where Ice Keese and a Silver Moblin will attack.
Go to the Sixth Destination
You can use Ascend from here, then make your way to the left side of the south edge of the castle, where you can float down into the door on B3. From there you can go to the sixth destination, where you will be attacked by Shock Likes.
Go to the Sanctum
After a brief custcene, the next destination is the Sanctum at the top of the castle. You can use Ascend at the end of the hallway where you fought the Shock Likes. From there, you can go northeast into the Sanctum.
Approach the destination, and there will be a cutscene. Then you must battle Phantom Ganon.