How do you get the hammer in the fire temple?

Okay, in that wide open room with all those curtains of fire that pop up to block you, you'll need to hit a switch to make it to door that another fire wall was protecting.

This first door is fake - Bomb it and move on to the next door, now you'll fight a Flare Dancer, once you Bomb him to death, the flame in the centre will go out and you'll be able to use that platform as an elevator.

Take the lift to the next room, next climb the one wall, then lay a Bomb over the ledge to activate the Switch and then climb the wall where the flame was and exit the room.

Now you're in a donut shaped room - climb the steps, hit the Switch and quickly use the inner edge of the hole in the center to make your way around to the Treasure Chest (don't fall down - it'll hurt) that contains the Megaton Hammer before the time limit's up!