Zelda 1 - Walkthrough of Dungeon 8 of Quest 1: The Lion (Zelda I NES mini)
Map of the labyrinth "The Lion": Dungeon 8 of Quest 1 from Zelda I (The Legend Of Zelda NES mini)

First, the map. The solution I propose doesn't take you through every room, but feel free to explore as you wish. When I was young, I would often get the master key from this level very early in the game to stop worrying about it. Along the way I would also pick up the magic book. This level is fairly straightforward as a maze since it has one large central artery running its full length.

First go left and kill Manhandla (1). Go left again and kill all the enemies to push the left block and go get the magic book (2). Return to the start and go right to get the key. Come back left and go up. No need to fight Manhandla in this room — just blast a hole at the top (3).

Zelda 1 - Walkthrough of Dungeon 8 of Quest 1: The Lion (Zelda I NES mini)

Kill all the Darknuts, take the key and go up, then up again in the next room. Avoid fighting the blue Darknuts and blast a hole at the top (1). Kill Manhandla to get Small Key and go up. Kill Gohma (2), go right and kill all the monsters in the room to get the master key. Go back left and go down twice. If you want the compass, go down twice and go right. Otherwise, take the right door (after finishing off the Darknuts) then the secret passage. Blast a hole in the top wall (3) and get ready to face the Gleeok.

The boss is a four-headed Gleeok. With the magic sword and all your life points he shouldn't be too hard to beat. Just hit his heads while avoiding his fireballs. Once you win, go up to collect the last piece of the Triforce.