The Goron Tunic
Use a bomb to stop the rolling Goron. Speak to him about the Dragon and the Gorons. He will ask you to rescue them and give you the Goron Tunic to aid you in your quest. The door to Darunia's room and the Goron shop will open automatically. Now enter Darunia's room and pull the statue at the back of the room to reveal a hidden entrance that leads to the Fire Temple. Make sure you put on your Goron Tunic or you won't be able to stay here very long because of the heat. Use the hookshot to get across to the bridge and Sheik will appear to teach you the The Bolero of Fire , then mysteriously disappear once again.
The Fire Temple
As soon as you enter, go forward. If you try to climb the stairs you'll quickly find that a flame wall blocks your progress. Jump onto the side banisters of the steps and jump back onto the steps above the flame wall to go up. Once at the top, you'll see that only one flame is burning and the others are all extinguished. Stand roughly at the top of the stairs and use Din's Fire, if you positioned yourself correctly all the torches should light up, opening the door up top. Go through.
Here, you'll meet Darunia, who tells you that the dragon Volvagia is the source of all the trouble. After he leaves for the boss room, jump across the platforms to the right and use your Hookshot to get to a bunch of pots and crates. Use Din's Fire here, which will light the torch stuck inside the Hookshot target, then pull out the bow and shoot an arrow to light the lone torch on the other side of the room. If you did this correctly, the gate should open, get across (with the Goron Tunic you can safely walk across the lava) and open the chest to get a Small Key.
Getting the Hammer
Exit the room the way you came from, jump down the staircase and go through the locked door on the right side. You'll immediately be greeted by a Keese and two Stalfos. Dispose of these enemies and the door ahead will open. In here, first raise your shield to block the floor tile attack, then get rid of the Iron Knuckle.
Go through the door that opens to meet the mini-boss of the dungeon, the Flare Dancer. You must use your Hookshot to pull the core out of him, and then strike it with your sword. After a while the core will jump back into the fire and the Flare Dancer will reappear. Repeat this procedure until he dies. You'll be rewarded with the Megaton Hammer. The next room gives you your first opportunity to use it - hit the rusted switch to open the gates and open the chest to get the Dungeon Map. On your way out you'll be ambushed by a Like-Like, if it eats your shield kill it and a chest containing a new one will appear.
Climbing the temple, 1F
The door leads back to the main room. Climb the stairs and use the Megaton Hammer to kick the blocks at the right wall out of the way, revealing a door. Go through to land in a large lava room. First, go to the large flame wall you see at the south. Climb the moving platform right in front of it and use Din's Fire to light the lone torch, which will make a bunch of Hookshot platforms appear across the room. Hookshot the torch to get through the flame wall, and bomb the wall behind it to make a door appear. Go through, and as you enter, use Din's Fire to make the gate open, which frees another Goron. Open the chest to get a Small Key.
Afterwards, go to the other side, i. e. the north. Jump across the platforms until you find one which launches you upward. It leads you into a cave, use Din's Fire here to light the torch and then use an arrow to light the other torch next to the locked door way down. This will open the locked door, so jump down and go through. In here, after enduring another floor tile attack, use your Hookshot at the large chest to get to it, then open it to get the Big Key. Use the torch on the other side to get through the flame wall, then exit the room.
Go to the locked door at the east and open it with your small key. Use the Hookshot at the grating to pull yourself to it, then climb it all the way up. Walk around until you're at either of the two sides and jump down onto one of the two platforms. From here, you'll need to jump on top of the block as (not before or after) it launches up, which requires a great deal of timing. It leads you to the next floor, so go through the door.
Climbing the temple, 2F
Go to the left and climb up the structure. Light up the big torch with Din's Fire and a Hookshot target will appear. Once you reach the grating you'll face a surprise attack by a lone Lizalfos. Kill it (or ignore it) and climb up the grating, then go through the door.
Climbing the temple, 3F
The maze you just ended up in is full of Lizalfos. Make your way to the south-west corner. Shoot the switch with an arrow (it can freely pass through) to open the gate, then Hookshot your way up. Jump across atop the maze and go to the north until you come across a cracked floor. Bomb it to reveal a large hole in the ground. Jump down and break all the crates here until you find a rusted switch. Hit it and the gates will open, open the chest to get the Compass. Climb back up to the maze afterwards.
Go to the northwest corner and bomb the wall to reveal an alcove with a switch. Go back to the south and grab a small crate from the alcove with the crystal switch, then take it all the way to the switch (you should kill the Lizalfos as they may turn out to be a nuisance) and drop it to open the door ahead. Step on the switch to free the Goron and open the chest to get a Small Key. Get back to the maze, climb back up and open the locked door at the west.
Go to the left and climb the wall to get inside the barred area. On the other side, Hookshot yourself up to the crate and pick up the small crate. Jump back down and drop it onto the switch to light some torches. Hookshot yourself back up and jump onto the grating. If you look above the caged-in area, you should see an unlit torch near the ceiling. Use the torches burning on the pillars and shoot an arrow to light the unlit torch, which will unlock the door. Jump across and go through the door, then follow the passageway to the next area.
In here, jump across to the platform in the middle and use your Megaton Hammer at the face in the middle to make it fall down. Now, unless you're hunting for Gold Skulltulas, you're done here - fall down the hole and use the newly created platform to get to the boss door.
Volvagia fights the same way he does in regular Ocarina of Time, so refer to that page for details.