You go to the Double Cog Cavern. Open the treasure chest in the southern area. Then you can leave by the southwest door. Look west then up and use your claw shot. Return to the middle of the cog room. There is a vine patch on the northern wall. Claw shot there and get random stuff. Then leave through the door on the ledge. The next room has water in it. Dive in. Swim northward until you get to the arch. There is a bomb fish, so swim up. Go back down and blow up the bomb rock. Swim through the resulting hole. Go down further and blow up the next bomb rock. Before you enter the second hole, swim up to the tunnel in the eastern wall. Open a chest for water bombs. Dive to the bomb hole and swim through. Take out your sword because there are enemies. Go through the door at the southern end of the room. There's other stuff in this room (rupees). Look up at the claw shot medallion. Hit it and lower yourself through a hole in the floor. The boss key is in the chest there.
Go to the room where you got it and drop down the little hole after in that area and you will be directly above the main room of the place where you fought the giant rammer in the beginning. then, claw-shot to the ceiling for the level you just dropped onto and lower down. DO NOT DROP DOWN! then, when you are below that level, use your other claw shot to fly over to the other lever, then equip your iron boots. this should start a wind in the next room. go directly forward and you can figure it out from there.
You get it in the sky temple when you beat the mini boss.
in the temple in the sky
Argorok the Dragon
When you beat the mid-boss, from the city in the sky.
The Snowpeak Ruins, the Temple of Time and the City in the Sky
you defeat the mini boss in the lakebed temple and the mini boss in the city in the sky
The thing is, you can't but, you can get a hookshot in the water temple and two hookshots in the sky temple.
The room where the key is is directly above the "main entry chamber" (the big one with 4 doors right near the beginning). You have to go all the way through the temple, as the bridges are out. You'll eventually reach a point where you need to double-clawshot your way across the missing bridge using those desert-helicopter-basket things. The key is in a tiny room with a big fan in the floor (same fan that's in the ceiling of the main entry room). You can stop the fan with a switch and jump back down through the hole to get back to the main room of the temple, and onward to the boss.
you get the second clawshot after you beat the sky temple's mini boss (note the mini boss is a beast known as an aeralfos) thereby getting the double clawshot
Clawshot to his tail then put the iron boots on to drag him down. After that you clawshot from one floating plant to another until you're behind him after he breathes fire. Then clawshot to his back and hit him.
the first one is in the water temple and the second one is in the city in the sky
you need to get both clawshots. you should find the other one in the sky temple. you can use an online walkthrough if you're lost.