Tail Cave is the first dungeon, which you can reach after finding the key in the Mysterious Forest.

Get a Key

Go to the west and raise your shield, then bump into the Hardhat Beetles to knock them into the hole. (You can also knock them back with the sword.) When they are gone, a key will fall from the ceiling. Take it.

Get the Compass

Go west to the next room. Go to the treasure chest, but be careful because there are Zols hiding in the floor around the treasure chest. Also, the torches in the corner will shoot fireballs at you.

Open the treasure chest to get the Compass.

Get a Second Key

Go back to the first room of the dungeon and go north. Use your shield and sword to knock the Hardhat Beetle into the pit, then step on the button. A chest appears. Open it to get another key.

Get the Map

Go east and kill all the monsters in this room (Stalfos and Keese). After they are all gone, a chest appears. Open it to get the map.

Get a Third Key

From the room where you got the map, step into the tile in the north wall that has a person shape in it. This is a one-way door. Go west and carefully open the chest that a Spark is spinning around. It contains a key.

Get 20 Rupees

Go west and kill the Mini-Moldorm. A chest will appear. (If it doesn't, kill the Mini-Moldorm east of there.) Open the chest to get 20 rupees.

Get the Roc's Feather

Go north to an area with a locked door. The Trap in the corner will rush toward you, so don't walk into its path. When the Trap is going back toward the wall, walk north and go through the locked door. You can also push up on the block near the Trap. This will block the path of the Trap.

After you unlock the door north of the Trap and go through, carefully follow the path, avoiding the spinning Sparks and the tiny Zols.

In the area with the owl statue, push the leftmost block to make the door open. Go through.

Use your shield to knock the Spiny Beetles upside down. While they are upside down, use your sword to attack them. When they are both gone, stairs appear. Go down the stairs.

In the underground path, go toward the left until you reach a ladder that goes up through the ceiling. Climb that ladder to reach the next room.

Go north, then walk close to the Traps to make them move toward you, then when they are going back to their original positions, go through them to the chest. Open it to get the Roc's Feather. Equip it and press the button to jump.

Get the Nightmare's Key

Go back the way you came. You can use the Roc's Feather to jump up and grab the flying heart.

Go back through the underground area. You can use the Roc's Feather to jump from platform to platform. Go east from the spiny beetle room. Then jump over the gap to the south of the owl statue, then go south to the next room. Go south until you see crystals to the south, but you don't need to break them. Instead, go east. In the area with the Stalfos skeleton and Keese, make sure that you are on the north side of the row of blocks. From there, go north.

Use the Roc's Feather to jump over the gap, then use a key on the key block. Go up the stairs and go west until you find a chest. Open the chest to get the Nightmare's Key.

Get the Stone Beak

Go back the way you came, to the area that is divided by a row of blocks. Go around so that you are south of that row of blocks. Then go through the locked door in the east wall.

Go north from this room and you will find some creatures with card suits on them. When you hit one, it becomes frozen. Hit the creatures so that all three have the same card suit displayed on them (i.e. all hearts, or all clubs, or all diamonds, or all spades). When all three match, they disappear, and a chest appears. Open that chest to get a Stone Beak. Now you can check on owl statues to get tips for completing the dungeon.

Reach the Mini-Boss

Go south, then use the Roc's Feather to jump over the gap and exit to the east.

Mini-Boss: Rolling Bones

Use the Roc's Feather to jump over the rolling spiky thing, then use your sword to hit Rolling Bones. Repeat the process until Rolling Bones dies. After this, a fairy appears, and a warp spot appears in this room. The warp spot is a shortcut back to the first room of the dungeon.

Reach the Nightmare

Go north from Rolling Bones's room. Avoid the Traps that rush toward you. Ignore the stairs. Go through the Nightmare's Door in the north wall.

Boss: Moldorm

Your goal is to hit the Moldorm's tail. Be careful not to let Moldorm hit you, because it can knock you into the pit and you will have to climb up and try again. Raise your shield to avoid getting hurt when Moldorm rushes around the room.

After Moldorm dies, it leaves a Heart Container. Take it to increase your hearts.

Get the Musical Instrument

Go north to the next room. Walk north to get the Full Moon Cello.

Afterward, you receive a hint about where to go next: Goponga Swamp.