Once you disembark, follow the path until you find a gossip stone. Hit it, and it tells you that there's an island in the middle of three boulders to the south of Molida. Remember this, as that island will come in handy later. Continue up the path to the mailbox, where the postman delivers a message from Astrid. Enter the second house from the left to find a piece of treasure. Enter the rightmost house and talk to Romanos in the corner. After he rants, head towards the exit. Romanos will call out to you before you exit, so talk to him again. He reveals that his seafaring dad came up with a specific path that let him get through the fog and that the cave next to the house was his dad's hideaway. Exit the house and enter the cave after a short interruption from Romanos' mother.
Head up the path, defeating the ChuChu and Keese that appear. Go up the stairs and jump the gaps to the right. When you jump off into a clearing, head north to trigger a fight with a River Zora. Quickly draw a boomerang path around the Zora and hit its back, stunning it. While it's stunned, hack at it with your sword to defeat it. Head all the way north to the door. Continue through the linear hall, defeating the Octoroks as you come across them. Now, back in the first room, use bomb flowers to destroy the bombable blocks and the crack in the wall. Enter the hole in the wall.
Open the chest to get a shovel. Tap the journal on the desk to read it. It states that the second hideaway is under the place where lines drawn through the tablets scattered across the island intersect. Hit the items icon and select the shovel. Dig at the cracked patch under the chest to uncover a big green Rupee, worth 100 Rupees. Head outside and go up the stairs.
There is a tablet out here, mark its location on your map. Go left and down to a chest with a piece of treasure. Go back to where the tablet was and run to the right and down to the next screen, where there is another tablet. Mark its position as well. Jump down and dig at the cracked patch of earth beneath the tree to uncover another huge Rupee. The other two tablets are near Linebeck's ship and the second house from the left. Draw lines between the east and west and the north and south tablets. Go to the intersection of those two lines, which should be a lone palm tree. Dig right under it to reveal a hole. Jump down. Read the journal, get the treasure map from the chest, and look at the drawing on the wall. Select the Sea Chart icon and draw the path shown on the screen onto your sea chart. Head west, then north to a door with a sun emblem on it. You can't open it now, but remember that it's there. Jump off the ledge to the right and make your way to the cave entrance. Go to Linebeck's ship and set sail.
The Southwestern Sea
Before pursuing the Ghost Ship to the north, go to the middle of the three boulders south of Molida. Stop by the island there and get the chest on the eastern edge of the field for a Courage Gem. Then, go to the Isle of Ember and dig up the cracked patches in Astrid's basement to turn up a treasure map and 20 Rupees. Head up to the third level of the island, to the right of the entrance to the Temple of Fire. Cut down the lone patch of grass and dig there to reveal a treasure map. Go to Mercay island and dig in front of the tree next to Oshus' cave for another map. Now, you can go to the Northwestern Sea and navigate the fog.
When you reach the Northwestern Sea, follow the path that you've drawn on your sea chart. Watch out for enemies and explosive barrels.
The Northwestern Sea
Now that you're free of the fog, head to the middle of the north end of the sea. You'll discover a small island.
Land on the island and walk around. Mark the locations of the four stone tiles on your map. A tablet to the north notes that you should draw a line connecting the eastern tiles and a line connecting the western tiles. The extensions of those lines will intersect somewhere, and you should dig there. So draw the requisite lines on your map and go to the destination indicated. The hidden treasure map is buried a few steps south-west of the bend in the path. Go up to the house in the middle of the island and grab a Cucco. You may have to chase it into a corner first. While you have it, run around the fence to the right and line yourself up with the ledge to the right. Jump off, and the Cucco's flapping should carry you across the gap. Open the chest for a Wisdom Gem. There's nothing left for you here, so head back out to sea.
The Northwestern Sea
Now go to the diagonal portion of the rock wall on the eastern edge to find another hidden island. Land on it.
The first thing you might notice about the island is that there's no map. It's up to you to walk the perimeter of the island and draw the map. As you draw the map, doesn't it look like the island is in the shape of a whale? That fact will come in handy when you hit the gossip stone near the middle of the island. It tells you that to enter the cave, you need to hit the four gossip stones on the island in a specific order. The four key words are rudder, spray, paddles, and sees. Thus, look at the map and hit the gossip stones in the whale's tail, spray, fins, and eye.
The gossip stones will tell you about six golden frogs around the sea who have the power to summon cyclones. Once the last one is hit, a bridge is extended across the water in the middle of the island. Dig right below the last gossip stone to score a treasure map. Enter the cave and go straight through to the end to reach the Golden Chief. He will bestow upon you a Cyclone Slate.
The Cyclone Slate is a great tool. By drawing certain shapes on it, your ship will be transported to a certain point in the sea. To be able to use these shapes, though, you must first hit the golden frog that patrols each area with the cannon. You have to lead your cannon shots a bit, or else you'll miss. There are three frogs you can get at now: there is one in the Northwestern sea north of the Isle of Gust. The two frogs in the Southwestern sea are northwest of Molida Island and between Mercay Island and the Isle of Ember. Once you talk to these frogs, write down their symbol on the sea chart and you can use these symbols to teleport across the sea. Exit the cave and leave this island.
The Northwestern Sea
Now head to the island to the north-east, Bannan Island.
Follow the path up to the house, killing all the enemies along the way. Speak with the old wayfarer in the house and learn of the mermaid that lives around Bannan. Head back outside and walk around the island, looking for the mermaid. When she appears, hit her with the boomerang to talk to her and find out the "mermaid" likes talking to wayfarers. Go back to the house and talk with the wayfarer. The mermaid hasn't turned up yet. Go outside and Ciela thinks that Linebeck may be the new target of the mermaid's affections. Go talk to Linebeck, then go to the wayfarer's house again. Talk to both the mermaid and the wayfarer. The wayfarer will give you a fishing rod, which lets you play the fishing minigame. Also, dig to the left of the sign next to his house to uncover a treasure map. Once you're done here, leave the island and enter the sea. If you visit a mailbox at least a day after visiting the Wayfarer, you'll get a ship part.
The Northwestern Sea
Set a course to the ship floating around the southern edge of the sea and board it.
Talk to the man on the ship twice. After the second time, you'll engage in a small minigame. The aim is to hit the "hero" as many times as you can before he can hit you three times. The basic strategy is to wail on the hero until he spins his trident around, then run away as he executes a thrusting attack. Rinse and repeat to get the desired number of hits. The first time around, the hero will give up after two times and give you a piece of treasure. If you exit and re-board the ship, you can "train" with the hero again, but this time he'll give up after 9 hits. The next visit, he'll give up at 13. After that, however, he'll go as long as you can last. If you break 100 hits, you will score a Heart Container. Subsequent attempts at besting your score will get you some treasure. Leave the ship.
The Northwestern Sea
Finally, you can get to the Isle of Gust. Set course for the island and land on it.