The Legend of Zelda/Underworld/Quest 2/Dungeon 4

Objectives

Obtain the Magic Book.
Upgrade your bomb carrying capacity.
Beat Digdogger.
Obtain a Heart Container.
Obtain the Raft after beating Digdogger but before getting the Triforce piece.
Obtain the fourth Triforce piece.

Walkthrough

Pre-requisites

Power Bracelet
Whistle
50 Rupee or Heart Container

Dungeon Walkthrough

The entrance to this dungeon can be found, not above the Lost Hills, but inside the very hills themselves. It is advisable to enter this dungeon with at least 150 rupees. The minimal amount is 50 rupees, required to pass through a room without losing a heart container. The extra rupees increase your bomb capacity.

This dungeon introduces separate red bubbles which will permanently prevent you from drawing your sword and blue bubbles which will restore that ability. If you touch a red bubble, you will have to find a room with blue bubbles if you want to continue using your sword. One such room is one room up and to the right of the entrance.
From the entrance, head to the left room. Defeat the Zols and Keeses to obtain a key, but avoid touching the red bubbles.
Return to the entrance and enter the top door. Now you must fight a Digdogger. Defeat it to open the door to the left.
Enter through the left door, and defeat the Darknuts and Pol Voices to obtain a compass.
Enter the room above. Fight past the Darknuts and unlock the door to the right. Go through the door and defeat the Aquamentus to open the door to the right.
Enter through the right door and defeat all of the monsters in this room. Push the left most block in the center row to reveal a stairwell that leads to the Magic Book.
Once you have the Magic Book, push against the top wall to walk through an invisible passage to a man who will sell you the ability to hold 4 more bombs in exchange for 100 rupees. The passage you came through is one way only.
When you are done, push against the left wall to discover another invisible passage. This one can be taken in both directions. If you defeat all of the Darknuts in this room, you will obtain a set of bombs.
Unlock the door to the left and defeat all of the blue Darknuts to obtain a key.
From this point, there are a couple of ways to proceed, but this walkthrough will cover a more thorough approach. Proceed through the top door and fight the Zols. Avoid the traps and enter through the next top door.
Defeat more Zols and obtain a set of bombs. The top wall may be bombed to reveal a passage, but walk through the right door instead.
In this room, all you can do is push the center block in the direction that you walk in. Do so and enter the bottom door.
Defeat all of the monsters in this room to obtain a key. Then bomb the right wall and collect the ten rupees. Return to the previous room and go through the top door.
Now push the center block up and bomb the right wall to reveal a passage. Walk through the passage and defeat the Dodongo to open the top door.
Go through the top door and defeat the blue Darknuts to obtain the map. Return to the room below, and through the bombed passage. Now push the center block left and proceed through the top door.
Defeat the Keeses and you will be rewarded with a key that you cannot yet reach unless you have gone ahead and collected the ladder from the sixth dungeon.
You can walk through an invisible passage along the left wall, but you can bypass that room and the hint room above it by bombing the top wall. You are forced to decide between giving up one heart container or 50 rupees in order to proceed to the room on the right. Never give up the heart container, so collect 50 rupees if you don't yet have that much and return here.
Enter through the right door and note the presence of the blue bubbles. Push the left block of the two center blocks to reveal a stairway to an underground passage. Return here if you touch the red bubbles on the other side of the passage.
Exit from the passage and avoid touching the red bubbles. Unlock the door above to encounter the boss of the dungeon.

Boss

The boss is a standard triple splitting Digdogger. Use the whistle and defeat it in the usual manner to obtain a Heart Container.

Walkthrough (continued)

Enter the door above the boss room to find the Triforce but do not collect it yet. Instead, walk around the Triforce wall and push against the top wall to walk through an invisible passage.
Defeat the Darknuts to open the door above. Go through and defeat the three Dodongos to open the door above.
Go through the door and defeat all of the Darknuts and Pol Voices in the room. When the room is clear, push the block that is located closest to the left door to reveal a stairwell. Take the steps to find the Raft.
Now you may return to the Triforce room and collect it. Keep in mind that the left doorway of the Raft room is a one way door. If you pass through it, you will not be able to return to the right.

Resupply

You can climb up the Lost hills to receive healing from a fairy.
Heading west three screens gives access to a medicine woman, provided you have a ladder.