The Legend of Zelda/Underworld/Quest 2/Dungeon 9

Objectives

Obtain the Red Ring.
Obtain the Silver Arrow.
Defeat Ganon.
Retrieve the Triforce of Power.
Rescue Princess Zelda.

Walkthrough

The entrance to this dungeon has been moved away from Spectacle Rock, to a very remote corner of Hyrule. Bomb the middle of the north wall of A-1 in Section 7.

From the entrance head up one room where you might encounter a man who will prevent you from entering if you have not collected all eight pieces of the Triforce. If you have them, you may proceed and enter to the room above.
Fight the Zols and avoid the traps. Push against the right wall to discover an invisible passage. Walk through the corridor, fighting the Keese along the way, and push against the right wall to find another invisible passage.
Fight the Wizzrobes and bomb the top wall to reveal a passage. Go through the passage and defeat the Patra in the next room to obtain the map. Then push against the left wall for an invisible passage.
Defeat all of the Wizzrobes and push the block to reveal a stairwell that leads to the Silver Arrow. Collect the arrow and return. (If you're desperate for a blue rupee, you can bomb the bottom wall, and defeat all of the Keese in the room to collect the rupee, then come back.)
Push against the top wall for an invisible one way passage. Avoid the red Bubbles and push the left block to reveal a stairwell to an underground passage. Take the passage and you will arrive one room to the left of the entrance. There is a blue Bubble in this room if you were hit by a red one.
Bomb the top wall and proceed through the revealed passage. Defeat the blue Lanmola to open the left door and obtain a set of bombs. Go through the left door and fight past the Like-Likes, while avoiding the traps, and proceed through the left door.
Defeat the Vires to obtain a blue rupee, and unlock the top door. Proceed through the door and fight the Keese. Unlock the top door and head through.
Push the center block up, and bomb the left wall. Go through the passage and immediately turn around and go back to avoid getting hit by a red Bubble. Push the block right and head through the top door.
Avoid the traps and fight the Wizzrobes. Proceed through the right door. Fight the Wizzrobes and bomb the bottom wall to reveal a passage.
Take the bottom passage and defeat all of the Zols to obtain a compass. Only return through the passage above as the rest are one way. When you get back to the room above, bomb the top wall and proceed through that passage.
Fight the blue Wizzrobes and unlock the right door. Proceed through and fight past the Wizzrobes and Like-Likes, and enter through the top door. You'll encounter a man who tells you to "go to the next room." Push against the left wall to find an invisible passage.
Avoid the traps and fight past the Like-Likes and enter the left door. Fight past the Wizzrobes and enter the top door.
You can defeat the Patra now or wait until you come back to the room. Push against the left wall to find an invisible passage. Defeat the blue Lanmolas and push the left block to reveal a staircase. Take the stairs to find the Red Ring. When you get it, push against the right wall to return to the Patra room.
Defeat the Patra if you haven't yet and push the left block to reveal a staircase to a hidden passage. You will arrive on the opposite side of the dungeon in a room full of Wizzrobes. Bomb the right wall to reveal a passage.
Go through the passage, and defeat the Patra to open the door to the right. Proceed through it, to encounter the boss of the dungeon. If you are not prepared to fight Ganon, push against the top wall to find a one way invisible passage and push the block you find inside to reveal another underground passage.

Boss

Ganon appears briefly before turning invisible. He travels in small circles firing energy orbs at you. Stab in to the space where you predict that he will be, and if you succeed in hitting him, he will appear for a short while before continuing the pattern. If you hit him four times with the magic sword, you will stun him and he will change color. At this time, you must fire a Silver Arrow at him to finish him off.
Defeat it and recover the Triforce of Power from Ganon's corpse. Continue to the room above and put out the fires with your sword and rescue Princess Zelda.

Resupply

Two screens east is a medicine woman, who can sell you potions.
Two screens east and one south of that is a shop that sells replacement shields.