When you enter the Eagle Labrynth, you'll see a door in every direction, but the north door is locked. You can get a key by defeating the Kesses in the west room and the Stalfos in the east. Get both keys, then use one of them to open that north door.

After heading two rooms north, go east to find the compass. This will show you where the Triforce is, but it won't help much until you get the map. Go back one room to the west and bomb the north wall in the center to make a door. The map is in the next room.

If you head two rooms west (you must defeat the Gels and then push the center block to get to the second room), you'll find an old man who'll tell you a hint about the "eastmost peninsula." He's referring to the furthest east room in the labyrinth where the Triforce is, as you can see with the map.

Go two rooms north from where you found the map - you should have the keys needed for the doors. In this room, you'll first meet the Goriyas. They're the strongest monsters you've faced so far, but your shield will easily block their boomerangs. Attacking them from behind or the side should work best.

In the next room to the west, you'll see a stairway surrounded by blocks. The traps in the corners will converge on you when you walk between them and take out a full heart if they hit you. You have to get around the traps on the north or south side to get to the west end of the room, so try this. Step slightly in the traps' path to spring them, then quickly back out of the way. As they're resetting, you can walk in between them. Push the westmost block to get to the stairs. Down the stairs, you'll find the Level One secret treasure - the Bow. You can't use this right now because you don't have arrows, but it will be a very important item later in the game.

Once you have the Bow, go back to where you found the map and open the locked door to the east. Defeat the Goriyas in the next room to get another useful item - the Boomerang. The Boomerang will stun many monsters and allow you to attack them more easily. It will also defeat very weak monsters like the Kesses and Gels. By now you should know that there are many items that are used with the controller's B button. The Boomerang is the best item to regularly keep active on the B button.

In the next room to the east, you'll hear the roars of the boss monster. Also, the Wall Masters will come out of the walls to attack you. If one of them grabs you, it will pull you back to the labyrinth's entrance, so watch out.

Open the door to the north, and you'll find the boss monster, Aquamentus. Your small shield won't stop his fireballs, but other than that, he's pretty simple to defeat. If your hearts are full, you can stand in the far west end directly in front of him and the door he's guarding and throw your sword beams - the fireballs should miss you. The best way to get him, however, is with bombs. Rush up to him in between his shots plant a bomb and get out of the way. Two bombs should finish him if you use them one at a time.

Once you destroy Aquamentus, he'll leave behind a Heart Container for you. In the next room, to the east, you'll find the first piece of the Triforce of Wisdom.