Swim and go through the corridor while avoiding the enemies, then take off your Zora Armor to swim up while avoiding the Baris.
Pick up the arrows in the chest east of the map, along with Water Bombs in the south chest, then climb the stairs. Stand in front of the handle and jump to grab it, which opens a gate. Open the door.
Following Midna's advices, use both the Hero's Bow and Bombs to shoot an explosive arrow at the stalactite near you. Follow the path, climb on the blocks, then shoot at another stalactite on the right to climb on it and even higher. To get another Water Bomb, fire an explosive arrow at the stalactite on the left, then climb to reach pots and open the chest. Then climb towards the door and open it.
Go ahead, get rid of the Lizalfos and open the door. You now stand in a big circular room. Climb down the stairs and go right until you reach the south of the map. Grab the handle to make the stair spin, then climb it. Turn to the left and lift the pot to find Ooccoo. Then go east of the map, grab the handle to make the stair spin, go down, turn right and pick up the Map from the chest.
Open the door to the west, hit the Helmasaur or avoid it, and open the next door. Follow the passageway on the right, shoot at the stalactite to the top and go ahead. Climb the vines to go right, them jump on the platform to the west and shoot an explosive arrow at another stalactite. Jump on it when it's up then towards the chest. Pick up the Small Key and leave this room to go back to the main circular room.
Climb the stairs, go west, unlock the door and open the next door.
Go left and find more Water Bombs in the chest. Then go to the other side and shoot an explosive arrow at the stalactite. Climb on it, then climb on the vines, go right and let go on the path. Then, grab the handle to open the door, let go and open the door to the north (on the map).
Jump to the central part, fight the Lizalfos and open the door to the south. Go left, find a Small Key in the chest and get out. Climb on the central part and get out. Go west, place a bomb next to the rock, go on and open the door.
Leave the monster in a bubble be and unlock the door ahead. Jump all the way down, then climb the vines and walk around the room until you reach the top. Pick up some Water Bombs in the chest, then climb one of the ladders. Grab the handle to make the water flow. Let go (you can come back for the chest later), then go towards the water to ride it to the bottom! Go to the central platform and grab another handle so the water flows further. Get out from the east and east again (where you got in). Go ahead a little and enter north again.
Now the big platform is spinning. Go left towards some pots, jump in the room underneath, then climb on one of the spinning round platforms. Jump north and open the door.
Go immediately left, pick up the Small Key and get out. Climb on one of the round platforms, jump west and open the door. Unlock the next door.
Put on your Zora Armor and your Iron Boots and go ahead.
You can find some Water Bombs and 20 rupees in the small corridors north and south. Place a bomb in front of the rock and go ahead. Take off your boots, avoid the enemy and swim right ahead. Take off your Zora Armor and swim up.
Mini-boss: Deku Toad
In the big room, get rid of the Toados, then look at the ceiling. There is the mini-boss! Get rid of the Toados using your sword, then run and try to find the shadow of the Deku Toad to know where it will land. Swiftly get close to its tongue and hit it several times using your sword. Then, before it climbs back to the ceiling, you can aim at its jaw and throw a bomb in it. If you succeed, it will not climb back to the ceiling and you can hit its tongue once more. If you fail, you will have to get rid of smaller enemies before being able to hit it again. Do this technique two-three times more to defeat it. Open the chest and pick up the Clawshot! If you want, use the Clawshot on the red dots (targets) in the room to find some rupees in the pots, then use it on the target to the south of the room and open the door.
Open the next door, jump on a round platform, jump east, get out and open the next door.
Once you're back in the circular room, you will notice that the water level rose. Climb the stairs then turn around and shoot the Clawshot at the target on the ceiling. Fall on the chandelier and open the chest to find a Piece of Heart! Jump into the water and swim north. Pick up 20 rupees/Letter K stamp in the chest on the central column, then shoot your Clawshot at the red target on the east side. The staircase will move and the water will now flow on it.
Open the east door. Get through the wheel's blades and open the next door. Go left and use the Clawshot on the target in front of you. Let go, then pick up the Water Bombs in the chest and shoot the Clawshot at the vines in front of you. Go right while on the vines and go down on the platform. Use the Clawshot again on the higher vines and then on the even higher ones, then go right to reach the northeast balcony and open the door.
Go right, shoot an explosive arrow at the stalactite above the right water column, then climb on it and jump on the tight "path". Jump to the other side, get rid of the two Tektites, shoot the Clawshot at the red target and open the door.
Press Z to aim at the enemy, use the Clawshot to make it get out of its bubble and hit it with your sword. Do the same with the other enemy, then use the Clawshot to aim at the vines on the ceiling, go ahead and fall down. Swim towards the vines, climb on it and get around the room while climbing up. Shoot your Clawshot at enemies to take their shell off and then hit them with your sword. When the way is blocked, use the Clawshot on the targets to go across. Once you've reached the top, pick up the Water Bombs in the chest, then climb one of the ladders and grab the handle to make the water flow. Let go, take a few steps, shoot the Clawshot at the target and find the Compass in the chest. Go over the fence, then slide towards the bottom. Get on the central platform and grab the handle to make the water flow further, then get to the ceiling using the Clawshot, go ahead on the vines and open the door to the southwest.
Get close to the water and aim at the head of the jellyfish with your Clawshot to get rid of it, then swim towards the west and climb on the other side. (There are 20 rupees in the chest at the bottom of the water.) Go through the wheel's blades and open the door to the north.
Climb on the big spinning platform, then on the other, then jump to the southwest. (There are 20 rupees in the chest.) Open the door, pick up 20 rupees in the chest, then go right, hook at the target on the ceiling to open the door, go ahead, open the door to the west and the next one.
Once back in the circular room, you will notice that the water level rose once more. Get down one level using the stairs or by jumping down, then open the door to the east and the next one. Jump on a round platform, then jump on a pillar a bit further and shoot your Clawshot at a target on the big spinning round platform. When you are all the way to the east, let go and open the door to the east.
Here you will need to change your outfit several times to swim on the surface level, swim underwater and walk at the bottom of the water. First, swim north, then walk to the bottom of the water, go through the gap (kind of arch), then go to the centre near a Bari. Defeat it with your Clawshot, them swim up a little, halfway to the surface, southwards. Look for a wall with a brown rock inside of it, close to a Bombfish, in the south part of the room. Put on your Iron Boots to be in front of the rock, then attack the Bombfish with the Clawshot to make it explode in front of the rock, or you can strike it and use one of your Water Bombs. Go through, swim south, then put on your Iron Boots and place a bomb next to another brown rock. Go to the far south and take off your Zora Armor to swim up. Get out of the water and open the gate to the south.
Get rid of the enemy in its bubble, then shoot the Clawshot at the target on the ceiling. Move down using the Clawshot, open the chest and pick up the Big Key. Put on your Zora Armor and Iron Boots and open the door to the east. Go across the corridor, swim towards west through the hole, surface and get out. (There are some Water Bombs in the chest.) Get through the room using your Clawshot on the targets and vines and get out to the west. Go west again.
You end up once more in the circular room.
If you want 50 rupees (Wii)/stamp (Wii U), put on your Iron Boots, climb the stairs, open the door to the west, go west twice, go to the top of the room with the spiral stairs, either by climbing with your Iron Boots, or by walking on the ledge, then climb one of the ladders, jump, shoot your Clawshot at the target and pick up 50 rupees/Letter Y stamp in the chest! before coming back to the central room.
To get a second Piece of Heart, go to the second floor to the east, grab the handle to make the stairs spin and thus make the water flow west. Take the stairs, open twice the door to the west, then jump on a round platform and jump on the small bridge (which has now risen). Go ahead, step on the switch, fight the Lizalfos, then from the switch, shoot the Clawshot at the target behind the chest and open it! Shoot again the Clawshot at the target on the ceiling to get out and come back to the central room.
Jump into the water and swim to the middle. Unlock the door, then break both pots to refill your hearts and to put a fairy in your bottle. Finally jump into the hole. Put on your Zora Armor and your Iron Boots to go down.
Twilit Aquatic: Morpheel
Stay away from the boss, look for its eye in one of its tentacles and shoot your Clawshot at the eye to draw it to you, then quickly hit it with your sword once or twice. When little fishes appear, try to avoid them, but if you catch one of them, get away or throw it at the boss. After hitting its eye twice, the monster will completely get out of the sand.
Take off your Iron Boots and try to follow him by swimming "behind its head". When you are close enough to its eye, use the Z lock and the Clawshot to hook its eye, then quickly hit it 3-4 with your sword. Do this twice more to defeat it. If you feel like the boss is going to swallow you, quickly put on your Iron Boots to get down.
After getting the third Fused Shadow, pick up the Heart Container and come back to Midna.