After restoring the power to the Spirits, you can now track down the Ghost Ship in the Northwestern Sea.
Ghost Ship 1F
After a cut scene, go left to go down the stairs into the ship.
Ghost Ship B1
Go to the left and a door will close behind you. Three poes will attack. Hit them with your sword to kill them. The nearby flames will go down. Go to the left and check on the girl there.
After talking to her, go north. Beware of Skulltulas hanging from the ceiling. If you get too close, they will suddenly fall down onto you. Go slowly, and hit the spiders with your sword when they appear.
Go to the right. You will find that the path is blocked by spikes. Equip the boomerang and use it on the crystal switch up above to lower the spikes. Go east and avoid the spinning flames. There is a poe in this area that will spit a fireball at you, so kill it if you can.
Go east, and you find some spikes that rise and fall on their own. Near the bottom of this area, a Skulltula will come down from above, so try to wait for it to appear, then kill it from a distance. Then go north past the spikes and hit the crystal switch to stop the spikes.
Go east and you will find some flames that seem to be blocking your path. However, you can just jump to the area below the flames. From there, go south, then east. Make your way past the rising and falling spikes, then hit the crystal switch to the north. Then go north into the room with the girl. Talk to her and she will follow you. Go south to leave her room, then open the chest on the left. It contains a triangle crystal.
Go west. The girl hates spiders, so if a spider appears, she will stop where she is, and you have to go back and get her. Throw the crystal to the area where you jumped from earlier. Jump across to where you threw it, then take it north and put it into the triangle pedestal to get rid of the flames. Go down and talk to the girl.
With the girl following you, make your way west and go into the red girl's room. After the sisters reunite, go to the east side of the ship and go down the stairs in the southeast area.
Ghost Ship B2
Go to the right and a Reapling will appear. They are similar to Phantoms. You can temporarily stun them by shooting them in the back with an arrow. Go east, then north, then northwest past the rising and falling spikes. Don't let the Reapling see or hear you. Use the northern path to go west. The Reapling stays in the southern path. On the west side of the ship, you will find a girl dressed in yellow. Hit the crystal switch behind you. Then talk to the girl. She tells you to open the chest on the left. Don't do it! The chest on the left contains a Rupoor, which takes 10 of your rupees away, and it also makes another Reapling appear. The chest on the right contains a Yellow Potion.
Talk to the yellow girl if you haven't already, then make your way to the east. There is a chest in the center of this floor that you can now reach (if you hit the crystal switch where you found the yellow girl). Open the chest to get the round crystal. Take it to the stairs that lead up to B1. If the girl is not with you, throw the crystal on the safe area at the stairs, then go get the girl. Then take the crystal and the girl upstairs.
Go north from the stairs and tap the circle pedestal to put the crystal in. Then go west and reunite the yellow girl with her sisters.
After that, go back down the stairs. You can now go to the southwest corner and go down the stairs there.
Ghost Ship B3
Go east past the switches. You can read the two signs. Then go to the southeast corner. The door will close behind you. Five Skulltulas will come down from the ceiling. Just stand still and wait for them to come down, then kill them.
After that, you can go north. You will see a crystal switch on the left, but don't hit it. It lowers the spikes to the steel drum area, but it also makes a Reapling appear, and if you try to go to the steel drum area, you will just fall down a trap door.
Go north past the crystal switch, then go through the first path on the left. A sign at the end has some numbers on it. Be sure to write those numbers on your map. Then go back down to the southwest area and pull the switches in the order of the numbers that you wrote down. If you did it in the correct order, the spikes above the steel drum area will go away.
Go to the steel drum area from the north side. There is a hidden switch in the left side of the steel drum room. Pick up and throw the barrels so you can reach the switch. Step on it to get rid of the flames to the west.
Go to the northeast corner of the area and then go west. Open the treasure chest on the way to get a purple potion.
From there, go south, then west, then north, and pick up the shaking barrel to find the green sister. Talk to her, and as you leave, she tells you not to shoot arrows at the Reaplings' backs.
Make your way back to the stairs, avoiding the Reapling if there is one. From B2, go east to the stairs to B1, and go west to take the green girl back to her sisters.
Stay near the south end of this area. Three of the sisters will shoot lasers in Link's direction. One sister will not. Stand in the path of the sister who doesn't shoot a laser. She will eventually shoot an energy ball. Hit the energy ball with your sword to hit the sister with it.
Eventually, one of the sisters disappears. This time, when a sister throws an energy ball at you, the sisters will bounce it between themselves, then throw it back at you. Watch where the ball goes, then hit it with your sword when they throw it back.
When there is only one sister left, she will spit three energy balls at you, but two of them are fake. Hit the solid ball. When the fake ones hit the walls, they split into smaller balls, so be sure to avoid those as you try to hit the real energy ball. After you hit the last sister twice, the battle will be over.
Take the Ghost Key, then open the chest to get a Heart Container. Step into the blue light, then go downstairs to B2. Go to the east side of this area and use the Ghost Key on the lock there. Go north and there will be a cut scene.
Your next destination is the island north of the Isle of Gust. However, it's not Bannan Island. There is another island north of the Isle of Gust. The island that you are looking for is west of Bannan Island. When you get close to it, Ciela will put it on your sea chart.
There is a sign at the north end of this island that tells you to mark the locations of the stone tiles on your map, then dig where the lines would intersect if you extended them. If you dig in the right place (near a palm tree) you will find a treasure map.
Go into Zauz's house and talk to him. After the cut scene, check the drawing on the wall and make a note of it. You will have to be able to draw this symbol without lifting the stylus, starting at the top of the symbol. The illustration below shows one way to do it.
1.8 / \ / \ /5___4\ / \ / \ / \ / \ 2____6.3____7
Now sail south to the Southwestern Sea, and go to Mercay Island and return to the Temple of the Ocean King.