When you arrive at Eldin, make your way east and south. You will come across some Mogma’s who pop out of the ground and warn you about their treasure. Go past them and make a left, watching for the lowering and rising lava around the platforms. Enter the cave there and a Mogma will give you the ins and outs of the bomb flowers. Blow up the middle pile of rocks and proceed down the tunnel to the end where a Mogma will tell you a person went in the opening of the rock in the center. Make your way around the right side and a creature called a Pyrup will crawl into a cave and blow out flames if you go close to it. Grab a bomb flower and roll it into the cave to take it out.
Go past there and you will have a couple Bokoblins to deal with before coming to another ledge. Look down and see two Pyrups inside skulls. Toss a bomb flower in the opening of each to destroy them. Now look across the bridge and see a plugged hole to the left of the bridge. Grab a bomb flower and roll it across the bridge to unplug the hole with an explosion.
Once you have blown the blockage open with the bomb, you can then hop across to the air spout going upwards and enter the opening and drop down to the ground below to the save there. Head through the corridor and talk to the Mogma who talks about problems with the Red Monsters. Head into the next room and clear them out by attacking the horn blower on the wooden platform to cease the non-stop assault of them.
When they are down, go back and talk to the Mogma and he will offer you rupees or a way forward. Choose a way forward and you will receive the Digging Mitts. Dig at the next X on the ground and you will uncover an air spout that will blow you upwards. When in the next area, there will be plenty of fire breathers blocking your path to the far right.
Grab the bomb flowers and just drop them at the side of the opening where the flames are coming out to stop the gush of flames. Head through the doorway on the far right and you will come out to an air spout that will take you back to the surface. Talk to the Mogma there and he will tell of a black figure that jumped the chasm. Walk over the bridge that extends and to the left will be a wooden long box. Toss a bomb flower behind it to reveal a chest.
Head through the passage on the left and follow the slippery slope up to the first platform. Kill the enemy there and you can hop over to the next platform on the right to toss a flower bomb down the hill to the destructible wall to find a goddess cube on the other side. To progress to the top of the sandy slope, fire your sling shot at the enemy at the top so that he drops his rock, and then run up.
When at the top, use a bomb flower to knock over the wooden tower and to blow open a cave between the two huts on the left to find Tubert and his game of Thrill Digger. There is also a stool there in case you want to replenish your hearts. Head across the tower bridge and climb up the vine wall and follow the path around. Head up the sandy slope by nailing the enemies with the sling shot and you will come to a locked door and 2 Mogmas chatting.
Now you will need to find the 5 pieces of the key to unlock the door. The first is to the left of the hole the Mogmas were talking in and the second is around the left corner, at the bottom of the hill under the tower. Knock it over with a bomb flower and dig it up. Notice the item on the ground there beside it. It’s a propeller that you’ll be coming back to get later on. The next key piece can be found in a destructible cave on the right of the sandy slope leading up to the locked door.
Underhand roll a bomb flower to the rocks to blow it open and then dig for the piece. The fourth can be found by knocking over the tower to the right of the temple door and following the path to a vine wall. Before heading after the key piece however, take the path directly across from the knocked over tower to find another Goddess Cube. When you head through the corridor to reach the vines, jump over to them, climb around to the entrance and step on the pressure plate to extend the bridge. Continue following the path upwards until you start to enter the red hot area.
Make an immediate right and jump down the sandy slope. Follow it to the right, all the way to the bottom and use a bomb flower to blow the next lava blockage outside a cave at the bottom. When the lava lowers, roll a bomb over to the rock wall and then enter and dig for the key. The final key can be found by taking the same sandy slope down in the heated area, through the right side cave, but by taking the right side of the slope and then hopping over two air spouts. Now that you have all 5 pieces, head back to the temple entrance and enter.