After Link gets the Magic Hammer, he can reach the Swamp Palace to the south.

Open the Path Forward

When you first enter the Swamp Palace, you will find that the path is blocked and you can't go farther. You can optionally check on the tile on the north wall and Sahasrahla will say that if you change something in the Light World, it also changes in the Dark World.

Go outside and use the Magic Mirror, then go into the building and push up the middle block, then push the left or right block to the side, and go north to the next room. Pull the rightmost lever to open the floodgate, then go south and step into the sparkling spot to return to the Dark World. Enter the Swamp Palace and you will find that this area has also been flooded with water, allowing you to proceed.

Get a Key

Swim northwest to the area that you couldn't reach before. Go north past the spike Trap and kill the Water Tektites. There is also a ball of water called a Kyameron that will float up and bounce around the room. Avoid letting it hit you. You can optionally freeze the Kyameron with the Ice Rod, then destroy it with the Magic Hammer to permanently get rid of it. Once the Water Tektites are gone, a chest will appear. Open it to get a key. Go north through the locked door.

Get the Map

Avoid the Water Tektites, Kyameron, and the fireballs that come out of the statue, and go to the end of the northwest passageway. Use a Bomb to break a hole in the wall. Go through and open the chest to get the Map, but be careful of the Zols that pop out of the ground along the path that you walked.

Get a Second Key

Go back to the previous room, and go south and pick up the southernmost skull to find a key. Use it to go through the locked door in the southwest of the room.

Get a Third Key

The yellow object in the center of this area is called a Yomo Medusa, and it will spit a fireball in your direction whenever you swing your sword, so be careful not to be in its path. Kill or ignore the Stalfos and Baris, and go west and down the stairs. Go through the north door and pick up the skull to find a key.

Get the Compass

Go to the previous room and go north up the stairs, and go through the locked door to the north.

Kill or ignore the Stalfos, and use the Magic Hammer on the Moles to the left of the lever. stand to the right of the lever and push it to the left to activate it. There is a cracked wall to the west, but all that you find beyond it is five rupees and a bomb.

Go south to the previous room. Get into the water and swim west to climb up the short ladder. Go west through the door.

In this large room, there are holes near the ceiling, and sometimes fish called Pirogusu will pop out and start swimming around in the water. Be careful to avoid these.

Go down into the shallow water, then go to the middle of the south wall and go through the door there.

Go east, then south, and go through the door in the south wall. Then go south and west, then north through the door there. Push the southernmost block to the right to make a chest appear. Open it to get the Compass. Then go through the north door.

Get a Fourth Key

Go up the southwest stairs and go through the door. Kill or avoid the monsters and go west down the stairs. The blocks to the left can't be pushed, so just go north through the door.

Pick up the skull and take the key, then go south to the previous room, go south up the stairs, then go east through the door to the large room.

Get the Big Key

Go up the northwest stairs and go through the locked door. Hit the crystal switch (your sword can reach past the barrier). Go to the right side of the lever and push it to the left. Then go to the right side of the barrier and hit the crystal switch to raise the blue blocks again.

Go east to the large room, and go through the southwest door. Now that there is water in the passage, get into the water and swim west to the other side. If you go to the skull to the north, be careful of the Zols that appear from the ground where you walked. Then go through the west door.

Kill or avoid the monsters, then go west and down the stairs. Push the southernmost block to the left, and push the center block up. Then go west, up the stairs, and go up the stairs in the north wall.

Push the block out of the way, and be careful of the many monsters in this room to go to the northeast corner. Push the block up or down, then fall into the hole east of where the block was. If your path to the east is NOT blocked by orange blocks, skip the next paragraph.

If the orange blocks are blocking the way, go west to drop down from the ledge, then go south and up the stairs, then east and through the door. Swim east, then go north past the blue line and hit the crystal switch there, then follow the directions from two paragraphs ago to return to this location.

Go east and open the chest to get the Big Key.

Get the Hookshot

Go west, and jump off of the west side to go down to the shallow water. There is a chest to the west, but it just contains a red rupee. If you want it, go back upstairs and push the block out of the way of the northwest hole and fall in. Open the chest to get the red rupee, then jump off of the ledge to the east.

Go south in the shallow water, go up the southeast stairs, then go east until you are back in the large central room.

Go up the stairs onto the platform in the center of the room and open the big chest to get the Hookshot.

Get a Fifth Key

While standing on the platform with the big chest, look east and use the Hookshot on the skull on the platform to the east. Lift the easternmost skull and take the key from under it.

Get a Sixth Key

Jump down from the ledge, then go up the stairs onto the platform with the big chest again. This time, go to the north edge of the platform and use the Hookshot on one of the skulls to reach the north ledge. Go through the locked door.

Go west and pick up the northwest skull to reveal a floor switch. Push the nearby statue onto the switch, but don't go through the nearby door that opens. Instead, go to the east side of the room and go through the door on the left.

Go north past the Bari (the Hookshot can kill it safely from a distance) and go down the stairs in the north wall. Push the lever to the left to drain the water. Go south down the stairs, then west through the door.

You can optionally get two hearts and 40 rupees if you go south and through the door there. Lift the skulls and open the chests. Then go west through the door to return to the previous room.

Go north, and go through the northernmost door.

The third block from the left can be pushed to reveal a chest that contains 20 rupees.

You can optionally go through the northwest door to find skulls that hide bombs, arrows, and rupees. After you loot this room, go south through the door to return to the previous room.

The second waterfall from the right hides a secret door. Just walk through the waterfall to go through to the next room.

Kill or ignore the two blue Bari, lift the skulls to get hearts, bombs, and arrows, then go up the stairs in the north wall.

Go south through the hallway with the blue Bari and the hidden Zols that pop out of the ground where you walked, and go through the south door.

Quickly jump into the water to prevent the Water Tektites from crowding around the ladder. Swim east against the current and swim onto the ledge with the skull at the east side of the room. Pick up the skull to get a key.

Go to the Dungeon Boss

If there are Water Tektites at the ladder, go to the east side of the ledge to lure them away, then get into the water and swim west. You can optionally bomb the cracked wall on one of the ledges to find skulls that hide hearts and other items.

When you are ready, swim west and go to the locked door. Go through it. Then go north through the door of the dungeon boss.

Arrghus

Arrghus's body is covered by small Arrgi that will sometimes spin outward. Keep your distance to avoid getting hit by them. Arrghus will also move slowly toward you, so move to a safe distance if it is getting too close.

Use your Hookshot to pull an Arrgi toward you. It will turn blue and slowly float back toward Arrghus. Hit the blue Arrgi with your sword until it is destroyed. Do this repeatedly until all of the Arrgi are gone.

Afterward, Arrghus will jump upward, then attempt to land on you. Keep moving until Arrghus lands and starts bouncing diagonally around the room. Hit Arrghus with your sword and it will jump upward again. Keep moving to avoid when it lands, hit it with your sword when possible, and repeat this strategy until it is defeated.

Collect the Heart Container and the crystal that falls from above. There will be a cutscene. Your hearts and magic will be filled and you will be sent outside of the dungeon.

The Hookshot gives you access to more of the Dark World, so it is time to search for treasure farther into the Dark World.