After you complete dungeon 7, you can continue on to the penultimate dungeon, known as Lion.
Go to the Dungeon
Go south from dungeon 7. You have to do this in order to be able to use the whistle to warp elsewhere.
A quick way to reach the dungeon is to use the whistle (but not in the same screen as the dungeon 7 entrance) until you reach Dungeon 2. Just stand outside and face the same direction each time you blow the whistle until you are outside of dungeon 2.
From there, go south, east, and south twice. Use the Candle on the one tree that is by itself in the middle. Go down the stairs to reach dungeon 8.
Get the Magic Book
Go west. You must defeat the Manhandla to proceed, so kill its mouths until it dies, collect the blue rupee that appears, then go west. Kill the Gibdos and Darknuts in this room, then push the leftmost block up or down, and go down the stairs. Get the Magic Book. Now that you have it, your Magic Wand's beams will turn into a fireball when they hit an obstacle, making it more powerful than before. This flame can also be used to light up rooms just like the Candle.
Get a Key
Go upstairs, then go east until you can't go east anymore. Light up the room with the Candle or the Wand, then get the key.
Get a Second Key
Go west to the first room of the dungeon, then go north. You can kill this Manhandla if you want a blue rupee, or you can ignore it. Bomb the middle of the north wall and go through the hole. Kill all the Darknuts to make a key appear. Take it.
Get the Compass
You can go east through the locked door and kill all the Pols Voices to get the Compass. Then go west to the room with the fireball-spitting statues.
Get a Third Key
Kill the Darknuts if you haven't already. This will open the doors. Go west.
Use the Candle or Wand to light up this room. Then get the key.
Get a Fourth Key
Go west and kill the Darknuts to get another key.
Get the Map
Go east and use the Candle or Wand to light up the room, then go east again. From there, go north. You can kill all these enemies to make a blue rupee appear. Go north through the locked door.
Bomb the middle of the north wall and go through. Kill the Manhandla to get the Map.
Get the Magic Key
If you would like some rupees and bombs, use a bomb on the middle of the west wall and go through. Collect the rupees and then go north. Bomb the middle of the east wall, then kill the Pols Voices to get bombs. If you haven't bombed the middle of the east wall, do it now, and go through the hole.
If you decided not to get the rupees and bombs, go north through the locked door.
Kill the Gohma to make the doors open. You can optionally go north and kill the Darknuts to get bombs. If you do, go south to return to Gohma's room.
Go east and kill the Pols Voices and Darknuts, then push the leftmost block up or down and go down the stairs to get the Magic Key. With this item, you no longer need to collect keys, because the Magic Key unlocks all doors and never disappears. It would have been more useful earlier in the game... After you have the Magic Key, it will just say "A" next to next to the key symbol in the top middle of the screen.
Go to the Dungeon Boss
Go upstairs from where you got the Magic Key. Then go west, then south twice. If the east door is closed, kill the Darknuts to open it. Go east. You can kill all these enemies if you want bombs. Then go down the stairs.
Follow the passageway until you are upstairs again. In the spiral room, bomb the middle of the north wall and go through.
Hit Gleeok's heads until they come off and start flying around the room and spitting fireballs. Ignore the flying heads and attack the ones that are still attached to Gleeok. When they are all dead, Gleeok dies. Take the heart container, then go north and get the Triforce Piece.