When you get back to the village, the Elder will tell you that there are three locks protecting the Fire Temple, and three monsters have stolen the keys. He tells you to talk to the villagers for advice on how to defeat the monsters. The guy who lives to the left of the Elder's house says that the monsters don't like a certain noise: one short noise, then one long noise. Another villager says not to chase behind them but to go straight into them.
The monsters will appear when you go onto the tracks surrounding the Fire Temple. Following the villagers' advice, go on a collision course for each of the monsters one at a time. Stun them by doing a short train whistle followed by a long one, and then when the monster is stunned, shoot it with the cannon to get the key.
After getting each key, the monsters will still harass you as you ride around, so go into the Fire Temple.
Use your boomerang on the Fire Keese in your way. The only path available to you is to go up to the three closed doors and then turn left and continue along the path. Be careful to avoid the spinning fire things around the spikes, and continue to the room at the left middle of this floor. There will be three stalfos. You can kill each one by throwing a bomb at it, but the sword will work if you have no bombs. Just hit it once to make it collapse, then hit its skull to kill it.
Go down through the door that just opened and hop down, avoiding the fire snake that is going around. The sign here says that the pitfalls in this area mirror the ones on the other side. Walk around making a note of the locations of the wooden trap doors. Draw corresponding marks on the right side of the map in the mirrored positions. Then go up the stairs marked with the red up arrow in this area.
Zelda will notice an old-looking vehicle. Jump in to be taken to a treasure chest with a small key in it. Go back into the mine cart and go back down the stairs.
Go to the short flight of stairs where you can hit the crystal switch across the way with your boomerang. This drops a round flat thing onto the ground. Pick up the round flat thing and throw it onto the lava spout to the right of the three doors just above the entrance. Hop onto the flat thing and hop across to the right side of the room.
There is a spout of fire ahead. Pull the block down twice, right once, up twice, then push it toward the right so it blocks the fire spout. Hop down to this area that mirrors the area on the left side, avoiding the spots where you (hopefully) drew marks in the places where the wooden trap doors were on the other side. Go around to the treasure chest to get a red potion. Go up the stairs to floor 2.
Get into the mine cart and hit the first crystal switch but leave the second one alone to reach a chest with a random treasure. Then go back and switch both switches before reaching the junctions. You will be face to face with a stalfos. Kill it, then open the chest to receive a second small key. Go back to floor 1.
Go to the three doors in the middle and unlock the two locked ones. Stand in front of the blue door and use the boomerang to hit both crystal switches in rapid succession. When the door opens, go upstairs to floor 2.
Floor 2, part 2
You will be in a room where you must fight Heatoise. To defeat it, you have to make it roll into the electrified Winders that circle the room. When you get close to Heatoise, it will retract into its shell and then roll toward you. Stand somewhere that will cause the Heatoise to roll into one of the Winders and get zapped. Then while Heatoise is stunned, hit its head with your sword. Repeat this process until Heatoise is dead. You will get the Bow and Arrows.
In the area to the right, use an arrow on the eye on the rear wall to create a bridge. Then hit the nut to receive more arrows. Cross the bridge and go downstairs to floor 1.
Floor 1, Part 2
Shoot an arrow at the blue thing below to hit the eye in the wall to the right, creating a bridge to the middle area. Hop over to the right to receive a random treasure from the treasure chest. Then hop back over and pick up the blue thing that you shot your arrow into. Tap the tile to the left to throw the blue thing onto that tile. Use the boomerang to hit the blue thing until it points up. Then shoot an arrow at it.
Cross the bridge that appeared and throw the blue thing onto the tile above you. Hit it with the boomerang until it is pointing to the left. Shoot an arrow at it to create a bridge. Go down the stairs to B1.
The door on the left has a cryptic sign that says that the only way to open that door is with a key. Go down the stairs to B2.
You'll immediately be attacked by stalfos on the left and right of the room. Kill them with arrows. One arrow will make them collapse, and one will kill the skull.
Use the nut to replenish your arrows, then go down through the door that opened.
Walk left and shoot an arrow into the blue thing to stop the lava on the right that is blocking you from using the whip poles. Run to the right and use the whip to whip across to the right side of the room.
Go up and kill the two stalfos, then carefully hop across the lava platforms to reach a chest containing a random treasure. Then whip your way downward. Step on the switch to open the door, then make your way to the left, avoiding the traps that go up and down. Get the treasure chest down below, then use the boomerang to use the Keeses' fire to light the two torches, making a lava platform fall down onto the lava spout. Hop across and go up to B1.
Floor B1, part 2
Shoot the Heatoises in the head with the arrows to kill them. The nut in the bottom left corner will replenish your arrows. Open the treasure and then make note of the signs in this room. Go downstairs to B2.
Floor B2, part 2
Kill the two stalfos then go past the switch and pick up the blue thing to the north. Put the blue thing in a position where it will hit the eye behind the door if you shoot at it. Then step on the switch and shoot the blue thing to activate the eye switch to receive a lava platform.
Put the lava platform onto the lava spout above. Then pick up the blue thing that you just shot into. Carry it onto the lava platform and drop it off at the upper level. Then wait for the lava platform to rise to the upper level, then tap it to pick it up and put it on the upper level.
Hit the bottom-right crystal switch to create a whip pole to the right.
There is a diagonal blue thing in the upper right. Put it onto the bottommost lava spout on this upper level. Then put the other blue thing onto the rightmost lava spout, and put the lava platform onto the leftmost spout. Rotate the diagonal blue thing to point at the other blue thing, and rotate the other blue thing to point to the left. Stand on the lava platform and hit the crystal switch with the boomerang. Then shoot an arrow at the diagonal blue thing, and then shoot an arrow from your lava platform to the eye on the left side after the timer starts when the right eye is hit.
Get the small key from the chest beyond the door that you just opened.
Hop down to the lower level, use the whip pole that you created to whip to the middle of the room, and go straight up to reach floor B1.
Floor B1, part 3
Use the key on the door on the left. Use the nut to replenish your arrows, then get into the mine car and hit the switches in the order 2, 1, 4, 3. Before going down the stairs, get back into the rail car and use an arrow to hit the secret crystal switch in the bottom left corner of the room (the boomerang isn't fast enough) and you will reach the stamp station. Then get back into the mine car and go down the stairs. Then just go down the stairs there to go to B3.
The sign to the left tells you which switches to hit, so make a note of them on your map. Pick up the bomb flower to the left and hop over to the right and use the bomb on the giant boulder. It will become a lava platform. Toss it onto the spout, then hop on and get into the mine cart. Hit the switches as you noted from the picture to the right of the stairs.
You will reach a platform with a sign that says to carry the Boss Key by cart. Before doing that, go down the stairs and whip over to a treasure chest, then go back.
Use the Whirlwind to blow the Big Key into the cart. Then get into the upper cart and both carts will begin moving. Shoot the switches as you noted on your map from the picture to the left of the stairs. If done correctly, you and the key will arrive together at the big lock. Go downstairs, read the sign to create a warp to the entrance, then go up to fight Cragma.