Get the Compass:
In the first room, head to the right, blow up the wall, and proceed forward. Enter and open the chest for 5 rupees. Proceed back to the entrance room and then run to the left side of the room. Place a bomb near the switch and then stand on the center platform in the room to proceed to the next door. Take out a bomb and throw it to the ledge above to blow up the window in order to activate a switch to open the door. Proceed forward.
In this room, you will notice that in the darkness, things will be revealed, but in the light, they disappear. That’s the main theme in the dungeon, so you need to be careful to balance light and darkness in these rooms to figure out what to do. Head north and place a bomb and toss it at the Helmasaur to pop its helmet off. Next, proceed forward and head over to the left and step on the switch to reveal a Small Key. Bomb the nearby cracked floor for something later in the dungeon, then Wall Merge to the key. Now go and open the door to the next room.
Head forward and use the Wall Merge ability to walk past the giant boulders. Use the Lantern to light the torches in order to see and then head forward and then enter the northwest room.
In the northwest room, you will see a platform going up and down. Get on top of it and then use the Bombs and toss them to switch to right and left. When both are lit, a chest will drop, containing the compass.
Get the Master Ore:
Now in the same room, stand on the platform and drop a bomb at a time where it will explode when it is fully down. This should blow up a hidden wall and allow you to access the room to the south. Here you will find a fairy fountain.
Now head back to the room before where the compass was and proceed to the next platform and head all the way to the east room. At the east room, you will see three Mimics (two green, one red). You can defeat them using most of your weaponry, such as the Bow or the Bombs, but I prefer using the Nice Fire Rod. Once defeated, it will raise and lower a platform. Once it is lowered all the way, you can access the room to the south.
There is a chest on the lower level that has a chest containing a Monster Tail. In the corner there is a place you can bomb, marked by the lines on the wall. Blow it up and then proceed to the room to the north again. Bomb the wall in that room and return back to the room to the south again. Open the lit chest for 50 rupees.
Fall down into the hole we blew up and open the chest in the room to get a Monster Horn. Navigate to the left and slash the torch to put it out to reveal the hidden floor. Navigate to the Small Key and toss a bomb at the Helmasaur and grab the key. Head to the south room and the camera will pan about. Head to south right room and defeat all the mimics to make the platform raise and lower as well as open the portal. Now return back to 1F and open the door near the stairs and proceed to 2F.
In the center room to the right of the boulders, there’s another floor you can bomb. Bomb it and fall down to grab a key. Go to the left room this time for a change to grab something. Slash the torch out so you can see the hidden walls. Navigate to the northwest part of the room and slash at the skull and step on the switch to reveal a chest. Get to the chest to obtain a Small Key. Head back the south end of the room.
In this room, place a bomb on the switch to the south, then wall merge onto the wall to the right with the face of a Helmasaur on it. Bomb the floor below and fall down to reach a chest containing 50 rupees. Head back to 2F and head the left route. In the west room, quickly head to the switch, let down a bomb, then head to the south door (you may need to Wall Merge if you aren’t quick enough).
In the next room, head south and then light the torch down there to light the entire room. Throw a bomb to the platform above on the west wall to open the window and let light shine down to the rooms below. Head to right and stand on the platform and hit the switch nearby to go to the next level in the room, head right and blow up the two windows to let in more light. Finally head back to the south platform, hit the switch again to lower the platform, then place a bomb on it, run up to the north platform, hit the switch with your sword, then wall merge on the north wall and it will flip. Open the Big Chest for the final Master Ore in the game. Place a bomb near the switch and merge into the wall to escape.
Upgrade the Master Sword:
Head back all the way down to the entrance and leave the dungeon. You can get back to the entrance by throwing a bomb to the switch to the left to move the platform.
Warp to the Lorule Blacksmith’s House with your Master Ore. Talk to the depressed Blacksmith and then walk down the stairs and he will ask to see your sword. Go into his house and talk to him again and he’ll upgrade your sword for two Master Ores. Once done, he will give you the Master Sword Lv. 3 (Golden Sword).
Get the Big Key:
Head back to the Dark Palace and take the portal back to B1. Head to the next level of the same room and head to the center room to the left; cross to the west side of the room and then hit the switch to let light onto the final eye switch to open the route to the boss.
Head to the left room and open the door. Head over to the left and you will see lines leading to some hidden switches. Toss bombs to the switches to drop a big chest containing the Big Key.
Proceed to the boss door and open it to fight the boss.
Boss: Gemesaur King
To start fighting the boss, light the two torches in the room to cause the Gemesaur King to appear.
Gemesaur King is similar to the Helmasaur King. You need to use your bombs and throw it into its face to break its helmet. At the same time, rupees will drop off of him. Throw about five bombs into his face to break the helmet off. Once his helmet is off, he is susceptible to sword attacks. With the Golden Sword, it will take two hits before he will surround himself in darkness. Once he does, relight the torches to remove the darkness. Three more hits from the Golden Sword and he will be down.