Now go through the door behind you (the one closest to you) and follow this passageway.  At the end is a room with a switch in the middle.  Throw Ruto to the other side and then step on the switch to raise the water.  Then join Ruto on the other side and follow the next passageway to a blocked door.  Shoot the thing hanging from the ceiling to unblock it and go through.  In this room wait for an elevator platform to lower and ride it up.  Don't try jumping to the small alcove with the white switch in it, you can't get to it yet.  Go through the door and you'll be back in the pit room (if you end up back in the first room you went through the wrong door).  Avoid the pits and go through the door on the opposite side of the pit room.  Now head straight right and hug the right wall until you find a switch and a blocked door.  Make sure you're holding Ruto and step on the switch to unblock the door, then go through.

Put Ruto down in the entryway of this room and venture forth to kill all the fish in the room.  Touch them to make them fly up then Z-target and shoot them with your slingshot .  You can also use bombs on them.  When they are all dead you'll receive the extremely cool boomerang!  The boomerang can get items for you and can kill most stuff at long range safely, such as those jellyfish, and with no worries about running out of ammo.  Anyway, pick up Ruto and leave this room then go straight, ignoring all side paths until you come to a switch and blocked door on the opposite end of the corridor.  Place Ruto on the switch so she'll hold it down for you and go inside. Kill the tentacle through the use of Z targeting and your new boomerang.  You'll receive the dungeon map as reward.  Now head out, retrieve the irritable Ruto, and take the first left and go through the door.  Kill all the bubbles using Z targeting and your boomerang before the time runs out and your reward is the compass.  Now head out of this room and head back to the room where you got the boomerang.  Take the side path right before the door to the boomerang room and kill the tentacle here.  Leave the room, take a right, then take another right and you'll be going down the center path.  Go through the door to find a third tentacle you have to kill.  Go back out the door and go straight and back through the next door to return once again to the pit room.

Now you have to fall down a certain pit.  It's to the right of you, but not the first one to the right of you.  It's a little more forward and right up against the right wall.  Fall down it and you'll find yourself in a room with a bunch of jellyfish and two gold skulltula's you can use for target practice for your boomerang.  Remember that you can use your boomerang to retrieve the gold tokens for you after the skulltula is dead.  Now go through the passage and door behind you to get to Bigocto's room.  Throw Ruto up onto the platform and then you'll have to fight Bigocto.

Hit him with your boomerang to stun him.  When he gets unstunned he'll start spinning around.  Hit him again and if you timed it right he'll have his back turned to you.  Slash him a few times with your sword.  Repeat until he's dead.