After you get the Red Candle in Dungeon 7, you should make preparations and then go do Dungeon 8.
Get the Magic Book
If you didn't get the Magic Book in Dungeon 4, you should consider doing that now. Just use the whistle until you are at a fairy fountain, then go south to find the Dungeon 4 entrance. Once inside, go north, then go west, then north. Go through the locked east door and kill Aquamentus, then go through the east door. Kill the Gibdos, Pols Voices, and Keese, then push the leftmost middle block. Go down the stairs to get the Magic Book. If you also have 100 rupees and didn't upgrade your bombs here (i.e. if you still can only carry a maximum of eight bombs), push the middle of the north wall until you go through, then pay to upgrade your bombs. To leave the dungeon, push the middle of the west wall to go through, then go west until you can't go west anymore, then kill the Darknuts and go south, then go south again, then east, then south to leave the dungeon.
Get Monster Bait
You will need monster bait to get through the next dungeon. The best price for monster bait is 60 rupees. To go to the shop that sells the bait for that price, use the whistle to warp to dungeon 1, then go east, then north, then east five times. Go north, then east twice. There is a secret passage north of the bottom-middle tree stump. Go up through the north wall there to find a hidden building. Go inside and get the monster bait for 60 rupees.
Go to Dungeon 8
To go to Dungeon 8, use the whistle until you are at a fairy fountain, then go south, then west twice. Use the stepladder to go onto the river in the left half of the screen. Use a bomb on the wall above the river to open a cave. (If a cave doesn't open, try bombing a different spot.) Go into the cave to reach the dungeon.
Go north. Try not to let a red bubble hit you, but don't worry too much if you do get hit. You can soon go to a room full of blue bubbles if necessary, although in order to proceed, you will have to get through this room without letting a red bubble hit you. Anyway, push the left block to reveal stairs. Go down the stairs. Go through the passage until you are upstairs.
If you did get hit by a red bubble, go east to reach a room full of blue bubbles, then push the leftmost block and go down the stairs, then go south twice to go back to the room full of red bubbles, then repeat the process, hopefully without letting a red bubble hit you this time.
After you reach the red Goriya room without getting hit by a red bubble beforehand, push the middle of the south wall until you go through.
Optional: Get the Map
If you want the map and don't mind backtracking, go east from the dodongo room, then bomb the middle of the south wall and go through the hole to get the map. Then go north and kill all the Goriyas and Keese, then push the leftmost middle block to make stairs appear. Go down and go through the passage until you are upstairs, then go south to return to the red bubble room. Push the leftmost block and use the stairs to return to the red Goriya room, then push the middle of the south wall until you go through.
Get the Magic Wand
In the Dodongo room, go south through the locked door. Wallmasters will come out of the walls here, so hurry to the middle of the room to try to stay safe from getting pulled back to the dungeon entrance. Then touch the wall to make a Wallmaster come out, then kill it. Repeat this until no more Wallmasters come out. Then push the middle rightmost block to make stairs appear. Go down to get the Magic Wand.
When you are back upstairs, go through the north door, then push the middle of the north wall to go through. From there, go east to the room with blue Bubbles. Push the leftmost block, then go down the stairs and go through the passage until you are upstairs.
You'll be in a room with blue Goriyas. Go north to a room with a Digdogger. Ignore it and go north, then equip the Monster Bait and press B to give it to the monster. Then go north, but be careful of the spike traps in the next room.
Light up the room with the Candle or the Magic Wand (if you have the Magic Book). Kill the Keese to get the Compass if you wish, then go north.
Get a Key
Kill the Goriyas. A key will appear, and the door will open. Get the key, then go west.
Get a Second Key
Kill the blue Goriyas, then go through the west door.
You can kill the Digdogger if you want a blue rupee. Otherwise just bomb the middle of the west wall and go through the hole.
Light up the room with the Candle or the Wand (if you have the Magic Book). Use the stepladder to go onto the water where you'll be safe from the monsters. You can kill all the Wallmasters in here if you want bombs. Otherwise, just go through the locked west door.
Kill all the Dodongos to open the west door, then go through.
Avoid the red bubbles and get the key if you don't have any keys.
Get the Magic Key
In the red bubble room, push the left block in the middle of the room, then go down the stairs.
On the other side of the passage, go west through the locked door. Kill all the
Stalfos, then push the block that is indicated by the X below:
O O O O O O X O O O O O O O O
Go down the stairs to get the Magic Key. This key opens all locked doors and never disappears. If only you could have gotten it earlier!
Go upstairs from where you got the Magic Key, then go east to the room with bubbles and Wallmasters. Go south to the next room. Push the middle block down, then go west. Push the middle of the south wall to go through. You can kill the monsters here to get a blue rupee. Otherwise just go east. Go through the narrow path and go east through the locked door. Then kill all the Goriyas. Get the bombs that appear, then push the leftmost block up or down, and go down the stairs, then follow the passage until you are upstairs.
Optional: Bomb Upgrade
If you have 100 rupees and want to carry more bombs, bomb the middle of the south wall and go through the hole. In the next room you can kill the Goriyas to get a blue rupee. Otherwise just go south. Kill Aquamentus, then go west through the door that opened. Kill all the Wallmasters in this room, then push the middle rightmost block. Go through the door to find the old man who is selling the bomb upgrade. From there, go east until you can't go east anymore, then go north to the room with three horizontal lines of blocks.
Get the Triforce Piece
Go north through the locked door. Kill the Dodongos with bombs, then get the heart container, then go north to get the Triforce Piece.