After you complete the Face Shrine dungeon, you get a hint to go to the mountain to find the next Siren's Instrument.

Learn Frog's Song of Soul

Go south from the Face Shrine and the owl will talk to you.

Then go to the area west of the Key Cavern entrance. You will find a phone booth. If you didn't already, you can dash into the tree next to the phone booth to get a Secret Seashell.

Then go south from there, and, in the Game Boy version, use the Pegasus Boots and Roc's Feather to jump over the gap, or in the Nintendo Switch version, use the Hookshot to go across the gap. Then read the sign across the gap and follow the instructions. Just go directly south from that sign to find the next sign. Keep following the signs. Each sign points to a sign that is in the same line vertically or horizontally as the previous sign, so don't get confused and check on a sign that is not aligned with the previous one.

After you have correctly completed the maze, stairs appear. Go down.

Go up to the big frog. Agree to pay 300 to hear their unreleased song. You will learn how to play the Frog's Song of Soul on the Ocarina.

Get the Flying Rooster

Go back to Mabe Village and go to the Weathervane north of Marin and Tarin's house. Push on it from below while you have the Power Bracelet equipped. The Weathervane will move, revealing stairs. Go down.

Follow the path and you will find the remains of the Flying Rooster. Play Frog's Song of Soul. The rooster will come back to life and start following you. Go outside.

Get a Secret Seashell

There are some holes to the west of the bridge to Kanalet Castle. In the Game Boy version, the only way to get across them is to fly over them with the Flying Rooster. In the Nintendo Switch version, you can use the Hookshot to go across. Go down the stairs at the end. The chest in the cave contains a Secret Seashell. In the Game Boy version, if you already got the L-2 Sword from Seashell Mansion, it contains 20 rupees instead.

Get the Bird Key

Now you need to go to the mountains. There is a warp spot in Tal Tal Heights. From that warp spot, go west until you find stairs leading up the mountain. Go up.

The owl will stop and talk to you. Lift a rock and go into the cave. Go through the straightforward path until you are in a room with crystals that you can dash through with the Pegasus Boots. If you didn't get the chest up above, use the Hookshot on it and open it to get 50 rupees, then in the Nintendo Switch version push down the rock below the chest and jump over the gap, or in the Game Boy version, use the Hookshot on the skull to the left. Or just pick up the Flying Rooster and fly across. Then use the Pegasus Boots to dash through the crystals to the east and go to the eastern area. Go out the door.

Go east until you find some water that you can swim in. In the Nintendo Switch version, you can dive at the base of the waterfall to get a Secret Seashell. Then go up the stairs that go up from this deep water. Go west, then go up the stairs to where there is a house. Go west to the broken bridge, then pick up the Flying Rooster and go west over the broken bridge. At the end, cut the bush and go down the stairs. Bomb the wall to the south and go through, then go east to the next room. You will find a Piece of Heart.

Go back to the house on top of the mountain. Go east from the house, then pick up the rocks to find a Secret Seashell.

Go back to the house, then go down the ladder and go east into the cave.

Go west in the cave and you will find a rock puzzle. However, you can ignore it and pick up the Flying Rooster to fly over the holes in the ground and go to the north exit.

In the next room, pick up the rooster, then float to the west area. Go over the gap and get the Bird Key from the ledge.

Reach the Next Dungeon

Go east until you can go south, then from the room with the rock puzzle, go east.

Outside, go east until you can't go farther east, then go down the ladder into the water. Swim east to the waterfall coming from above, and dive there to get a Secret Seashell. Then go east and go into the cave. Bomb the north wall and go through to find stairs. Go up those stairs and follow the path to reach some treasure chests behind rocks. All of the treasure chests contain Zols, so ignore them all and push the upper left rock to the left, then the one below you down, to go outside. Open the chest outside to get a Secret Seashell. In the Game Boy version, if you already got the L-2 Sword from Seashell Mansion, it contains 20 rupees instead. Then to back into the cave, go north and go down the stairs, then go south, and continue going east.

When you get outside, keep going east. In the area with an owl statue, go up the stairs and into the cave. Go through the cave. When you get outside, go west and into the next cave. Go through it and go down the stairs. Jump over the hole, then go up the stairs and go east. Use the hookshot to go over the gap, then jump down from the ledge to reach the door to the outside.

Bomb the cracked wall to find a Fairy Fountain. In the Nintendo Switch version, you can use the shovel to dig in the middle of the small stones on the ground to reveal a warp spot. Then go into the northeast cave. Follow the path through it and you will be on top of the mountain. Go west and lift the rocks, then in the Game Boy version, push on the keyhole to use the Bird Key, and in the Nintendo Switch version, press A to use the key. Then you can go into Eagle's Tower.