Kill the Zols that pop out behind you and go to the hole in the floor. Hookshot across. (This dungeon entrance reminds me of the Shadow Temple in Ocarina of Time.) Go down the stairs.
You will be encountering Wizzrobes for the first time in this dungeon. They stand in one place and reappear and disappear, shooting a beam in the direction they're facing that you can't deflect with your shield. You must kill all the enemies in this room, avoiding the Beamos's beam. Once you do, the door opens. Go through.
Go down the steps in front of you, and head north, then west when you can't go north anymore, then at the end of the barrier above you turn north again. Enter either of the top two passages and go through the open door.
Beware: the lamps in here shoot fireballs every few seconds. Push the block to either side and go through the north door that opens. Keep going straight up until you reach a treasure chest on a wooden bridge. Open it for a small key. Return to the room with the fireball lamps, pushing the block down to get out. Exit east.
Pick up the top-left pot for another small key. Then put on the Magic Cape (the Beamos won't shoot at you with it on) and walk onto the spikes to pick up the skull and step on the switch below, revealing a chest. Open it for a third small key. Go through the locked door in the north wall. In the next room, exit north again.
The straightforward path takes you to a large room where a Wizzrobe is right in front of you, so get out of the way. Two statues will be shooting fireballs at you; be careful. Pick up a skull above you and go left through the narrow passage with walls sticking out (make sure you don't get hit by a circling fireball). In the corner at the end, hit the crystal switch to turn it blue. Before leaving, pick up the skull for another small key. Go back through the narrow passage until you reach the door where you entered. Go through it and follow the path until you're back where you used the Magic Cape to walk over the spikes. Exit through the door in the south wall.
Open the chest for the map, dodging the fireballs, then exit through the locked door in the west wall. Go down the stairs near you, then make your way to the upper-left of the room, and go up the stairs here. Go around the edge of the room, heading south until you can walk onto the mesh floor. Walk north and pick up the skull here to reveal a switch, which makes a chest appear. Open it for a small key. Then head south down the mesh, and go through the bottom-left locked door.
Leave the crystal switch alone; it should be blue. This room has a yellow thing that shoots fireballs when you swing your sword, so be careful not to get in its way. The eerie floating skulls take a lot of hits before they die. Use Magic Powder on the Bubble if you want to get rid of it. Kill the Bari to get another key, and exit through the locked west door.
The tiles in this room fly at you, like in past dungeons, and there is a fireball-spewing statue. You are ALMOST safe in the doorframe, but you should adjust your position to get a little farther back, because one of the tiles may still get you if you're too far into the room. If you're positioned correctly, the fireballs will be deflected by your shield, and the tiles will not hit you. Once all the tiles are gone, go around and light the torches with the Fire Rod (you will get a free magic refill in a moment). Go north through the door that opens, and open the chest for the compass.
Go south to the flying tile room, and south again to the next room. The slugs on the conveyor belt randomly drop bombs, and there is a Wizzrobe to the left of where you entered. If you want to kill the Wizzrobe, be careful not to stand in the path of the yellow, fireball-shooting thing. Go along the conveyor belt to the other side of the room, and pick up the skull in the top-right corner for a large magic jar. Kill the red Bari if you want and go up the stairs.
Four Wizzrobes will appear above, below, and to the left and right of you (they will move according to where you're standing). They keep regenerating no matter how often you kill them, so you just have to avoid them.
You will have to light both these two torches and the two torches in the next room, but to get to the torches you have to move the blocks. Push the top and bottom blocks to the side, and then push the center block up or down. Do this in the next room as well, then light all four torches with your lamp (the Fire Rod is not necessary; it consumes more magic). Once they are all lit, you will hear a rumbling sound for a while (it goes on so long that the torches go out, even). Exit east from the bottom room to a room with a mesh floor and a hole below some spike traps. (The Sahasrahla tile above just tells you to light the four torches, which you just did.) Drop into the hole.
Open the chest for the Big Key! Then exit the only way you can go, west. Walk onto the orange warp tile, go north through the Big Key door, and step on the orange warp tile here.
There is a Big Key door in this dark chamber; ignore it for now and exit east, then south through two rooms, until you're where you got the map (there's a fireball-spewing statue here). Jump down off the ledge, head south, up the stairs, and exit east.
QUICKLY use your hookshot on the block across the way and dash up the narrow path, which will crumble like in the Palace of Darkness; creepy eyes on the wall will also shoot lasers as you pass, but they won't hit you as you dash past. Once at the end, open the Big Chest for the Cane of Somaria. With this, your inventory is complete! This magic cane will create an orange block that you can push around and even pick up and throw; very useful for switches that won't stay down. If you've already made a block and you use the cane again, the block will disappear and four fireballs will shoot out from where it was in each direction. You can then create another block. It does use magic, so don't overdo it.
Exit the only way you can go: west. You're back where you got the map before. Go north, and north again through the next room, and then jump off the ledge in the room with the mesh and exit west to where there's a Big Key door.
Be careful of the Wizzrobe that appears and go through the Big Key door. There is a skull to the left hiding a big Magic Jar to refill your magic for free. Go north along the wooden bridge and down the stairs in the north wall.
Everything is dark, now. Four fireball-spewing statues are out there in the darkness, so watch out. Lift the skull in the upper-left corner to find a switch that won't stay down. Now you get to use your newly-acquired Cane of Somaria! Create an orange block and push it onto the switch. The door at the bottom-left opens, so find it and go through.
Still dark. Simply exit west, avoiding enemies. In the next dark room, go north to where there's a spike trap. When it passes, go into the next narrow path below. Once you get to the third narrow path, go straight down and pick up the skull pot to get to the bottom of the room, where you are free to move towards the left. Go north and you find a yellow, fireball-spewing thing, conveyor belts, a crystal switch, and a fireball-spewing statue somewhere above you in the darkness. Use your hookshot or boomerang to make the crystal switch turn orange, then go back down and through the bottom-left door.
With the orange blocks down, you can move west into this room. In the center of the north wall is a crack you can bomb, so do it, but be careful; some tiny black creatures will periodically scurry south from the hole you made. Go through the hole, turn the crystal switch blue, and go back to the last room. Exit west.
It's light again. Zols will fall randomly from the ceiling; stay out from underneath them. Move into the room and get behind a block so the yellow swirling thing doesn't hit you. Avoiding the enemies, make your way to the north of the room (along the right side of the room to avoid a Bubble) where there is a crystal switch in a narrow path. Turn it orange, then go up the stairs below you.
IMMEDIATELY head right to avoid the flame snake. Avoid the Bubble as well and head west to the boss door! Go through to discover...
-- Vitreous --
Ewww; a slimy eyeball! Get into the bottom-right corner of the room. The smaller eyeballs will come floating out to you (gross); slash your sword like crazy to kill them (if you slash fast enough, they won't touch you). Vitreous periodically floats up above the slime (turning white) and shoots lightning straight down (like Agahnim). In the corner of the room you will be safe. Keep killing those small eyeballs until they're all gone. Then Vitreous will surface above the slime (yuck) and start bouncing towards you! Break out your bow and arrows and shoot Vitreous eight times to destroy it! Get inside the explosion to grab the piece of heart, then stand in the center where the crystal will fall!
The maiden inside says a lot of stuff you know already, and also that Agahnim is simply Ganon's pawn. She says Zelda is waiting inside Turtle Rock! As always, your hearts and magic will be filled, and you're returned to the outside of the dungeon.