Hover over to the platform to your left.  Then on to the one with the switch.  Step on the switch, hover back over to the previous platform, continue on to the one in front of you (that still has a silver rupee on it), then turn left and hover to the middle platform, then continue in that direction to the platform with the silver rupee.  Immediately turn around and hover back to the middle one, then on to the next one with the silver rupee.  Use your hookshot on the target above the high door to reach the last rupee and open the blocked door.  Hover over to it and go through. Take off your hover boots now.  Stand on the red tile and play the Song of Time, then put on Iron Boots and drop down.

Once at the bottom, kill the clams with your hookshot and start collecting silver rupees.  For some of them, you'll have to stand under it and then hookshot to one of the hookshot targets on the wall.  You'll have to aim right so that you'll hit the rupee on the way up.  Try standing almost right under the rupee.  You can also try taking off your boots and swimming to it but you'll be swept around by the current.  The highest one is too high to use the hookshot targets so you'll just have to swim around the ceiling to get it.  Be careful to avoid the middle of the ceiling or you'll be swept up and have to put the Iron Boots back on in order to get back down.  Once you've gotten them all, float up to the surface and get the small key that's now there.  Go back through the door.

Back in the lava room, use the hookshot on the torch by the high door to get up there.  Go through this door.  If you kill the enemies in this room you'll get some arrows.  Take out your hammer and start smashing all the statues around the walls.  One of them has a switch under it.  Step on it to remove the fire pillar and get the small key.  Another has a gold eye on the wall behind it.  Shoot the eye to unblock another door.  Go through this new door.

In this room you have to stand on the side and shoot the eyes of the 4 statues.  You have to do it in one pass, if you miss one you'll have to do them all again.  Once you do the room will stop rotating and a chest will appear.  Shoot the chest with your hookshot to get over to it.  Another key.  Now use your hookshot on the target on the wall to get back up.   Go back and make your way back to the first room.  If you're low on health or magic, go stand in between the two pillars where Navi turns green and play the Song of Storms for a Big Fairy.

Now go through the lion head on the opposite side of the room.  In the first room kill the two Stalfos, get the fifth key, then go through the next door.  In this room, take the first left, then go left again and grab the rupee.  Turn around, go up the hill (you'll probably be smacked by a boulder on the way up) to the very top for another one.  Now go back down and a ways and take a left.  Turn right and you'll see a rupee floating in front of you.  Jump off the ledge to get it..  Walk forward a bit, look up and hookshot to the target above you for another rupee.  Turn around, take a right, take another right, and another right for the last rupee.  Turn around, go up the hill, take the left, then turn right and use the hookshot target on the ceiling to get over the flame.  Go through the door.