Go ahead and jump the first set of floating rocks, then turn left and jump another one. Talk to the Mogma here, then head back and turn left. Wait for the platforms to descend then jump onto them. Wait for them to rise again to be able to reach the other side. Cut the two ropes with you sword, and use your Beetle for the third one on the wall, next to the bridge.
Once the Lizalfos is taken care of, use your Beetle to hit one of the bombs on the stone head in the lava. The eye of the head will roll towards you. You can now ride it across the lava.
Ride the ball to the right side. Ledd will pop up, asking you to bring back his bomb bag. Crawl through the opening to the left, next to the loose wall. Roll a bomb flower back through the opening to open up the way. If you want to pick up some goodies, climb the ladder here, and get the Amber Relic. Don't go back yet though, drop down the the fence surrounding that area and walk across it to another platform with two digging mounds. Here you'll find some Elding Ore and a fairy.
Once you're ready, head back through the opening and into the newly opened room. Defeat the Lizalfos and open the chest.
Hop back onto your trustworthy circus ball and make your way to the opposite end of the room. Throw a bomb on the rising platform just as it is about to go up. The important part is that the bomb explodes while it's up, so that it blows up the wall. Inside of the chest you'll find a golden skull.
Jump back onto the ball, and push in the target-like pillar that is sticking out of the path leading north. This will raise on the platforms, but still it's not enough to get up that path.
Lastly, using the rock ball, go to the top left corner of the room, where a chest sits on a platform. Inside you'll find a blue bird feather, another item used in upgrades. Finally, get onto the cenral platform, then up the western stairs. Throw a bomb on top of the rock blocking your path, and dispatch of the Lizalfos on the other side. Enter the new room.
This room requires you to jump across the sinking platforms. The bottom right and top left one are solid, so you can stand on those. One of the platforms rises using a lava stream, ride that up to the three Bokoblins and the chest with the dungeon map.
In the central hub room, go to the eastern wall using the rock ball, the apparent dead end next to the area where you got the Bomb Bag. If you look closely you'll notice a small crack on the wall. Two bombs will blow it wide open, allowing you to continue. Just before the platform with the Bokoblin, on the left wall, there's another crack just like the previous one. Two more bombs to blow it open, then continue onward.
Eventually you'll reach a red, closed gate. Use the Beetle to cut the two ropes and open it. To reach the rope on the other side of the gate, navigate the Beetle through the corridor behind the bird statue on the elevated ledge. Wait for the next lava stream to subside, then go through and across the physically impossible lava bridge.
You'll be back in the central chamber. The ledge with the Lizalfos has a chest containing 20 rupees. Your job here is to push the second pillar into the bridge leading north. This will lift up the platform allowing you to get there.
Sprint up the slope, dodging the boulders that drop down. There's an indented ledge on the left wall where you can restore you stamina. Once you're up, crawl through the opening, and go up the stairs. Throw a bomb onto the slope in such a way that it hits the grey, damaged area. It'll roll down and blow up a wall, exposing another ledge where you'll be able to rest your stamina while sprinting up.
Go back down and do just that - sprinting into the alcove to avoid the boulders and restore your stamina. Once up, turn left and sprint up the narrow path to reach a chest with the Dragon Sculpture. As you go back a boulder will drop from the dragon's mouth and chase you. Sprint back down and the boulder will rocket into the other dragon mouth, blocking the lava flow and allowing you access to the boss room.
Rotate the dragon in such a way that it fits the hole - the dragon's head should be in the bottom right corner, facing down.
Once Scaldera is defeated, head up and into the Eldin Spring area. You will receive the Amber Tablet after the cutscene.
Just as last time, head back to Skyloft to open up a new area.