After Fi's warnings, take a look at the Bird Statue, then go ahead and notice a Goddess Cube lying lower to the left. Perform a Skyward Strike to make the cube take off, then go back on the path and head northeast. Jump on the flat rocks and meet two Mogma. Speak to each of them to get more information about Zelda, then go on your way. Get rid of the Red Chuchus (take note of a red rupee at the bottom of the vines on your left), then of the Fire Keeses. At the crossroad, go left. Talk to the Mogma to get information concerning Bomb Flowers. Practice at throwing them around and making them roll, especially roll one of them into a small passage to the right which contains five rupees, and throw one of them at the cracked wall on the left, which reveals a new passage. Get into the "house" in the middle where one or two Volcano Ladybugs can be found, and that you can catch if you bought the Bug Net. Then, get in the revealed passage.
Once you got out, take a look at the Bird Statue, then go on and talk to the Mogma who saw Zelda in the neighbouring cave. Keep going east and you will notice a strange creature... Jump lower, pick up a Bomb Flower and make it roll in the hole so the flames die out. Then, keep going this way, climb up and fight the Red Bokoblins. Go ahead and jump towards the Bomb Flowers. If you want to, you can throw Bomb Flowers into the hole in the two enemies' shells, which isn't always easy. Cross the bone bridge by dashing to prevent you get hit by the lava, then talk to the Mogma to learn about the dam system. Go back across the bridge, pick up a Bomb Flower and make it roll on the bridge so it explodes upon touching the lava! The lava will flow and free new paths. Cross the bridge again, get one floor higher and go down right in front of you. Go left and climb on the steam geyser to fly up to the cave's wire fence!
Jump down (don't forget to use your sailcloth), then go left and speak with the Mogma who is complaining about "redlings". Go straight ahead and fight off the Red Bokoblins, but their leader will summon more of them. Climb on the wired crates and attack it. Get rid of the remaining Bokoblins, then come back to the Mogma. Tell him that you would like to go further and he will give you the Digging Mitts! Following his advices, dig the ground on the crossed slicing marks to fly to the higher level! At the crossroad, turn right and you will reach a big room. Go to the southeast corner while avoiding the flames, then pick up a Bomb Flower and make it roll into the hole to the north. When the flames are gone, go right. Dig where you can see a cross in front of you, then fly and go towards the big steam geyser to end up outside! Talk to the Mogma to the north who saw a girl dressed in black crossing the gap, then go in this direction. A bridge will be created and the woman in black will call you.
Cross it and take a look at the Bird Statue, then head straight ahead. Jump on the flat rock and dash to cross the sand slope until you reach wooden planks. Fight off the Bokoblin, then take a look at the Bokoblin on higher grounds which is waiting for you with a giant rock. Launch your Beetle at it, then while it's going to grab another rock, run to it, climb and strike it. Go right, get rid of the other two Bokoblins, then go ahead towards the two Bomb Flowers to the left. Locate the big tower with a Bokoblin at its top, then pick up a Bomb Flower and drop it at the tower's base to create a bridge once it collapsed! Get on the bridge and go ahead. Climb the vines, then follow the path to the right, and here is another slope with Bokoblins awaiting you. Dash to the middle and climb on one of the wooden buildings. Attack the Bokoblin standing there, then keep on climbing while staying on the outer borders to avoid the rocks. Launch your Beetle again at the closest Bokoblin, then as soon as it flees, rush, climb on the ledge, then even higher.
Two Mogma are talking about a key broken into five shards buried around. They saw Zelda again! Take a look at the Bird Statue then Dowse to look for the key shards. Go left and dig not too far to discover the first Piece of the Key. Go on to the left, get close to the edge with the bombs and throw one of them at the tower downward. Slide towards the fallen tower and dig where it used to stand: second Piece of the Key! Notice the kind of propeller close to you, then go back to the plaza in front of the great door. Get close to the Bomb Flowers, then throw them at the three Bokoblins or attack them with your sword if you didn't take care of them before. Next, throw a Bomb Flower at the huge rocks downward to the left to blow them up. Slide down to the wooden structure, then climb back where the rocks exploded and dig the ground to discover the third Piece of the Key! Go back to the top, go right near the Bokoblin camp and find some Bomb Flowers under a tent. Make one roll towards the tower where the leader is standing, then climb on the fallen tower, cross the gap and go on.
Go on until you reach a building. Look left towards the Stamina fruit, hang on the ledge and go right. Climb to the left, jump to the other side and go ahead up to the two hearts. Dash, jump towards the vines and grab them! Move right, pick up the Stamina Fruit, then go to the top, to the left and let go. Get in the building, then step on the switch to activate the bridge. Go straight ahead, into a very hot area. Use your dowsing ability to understand that you have to reach the south, then run to the right and head into the tunnel! Do your best to stay on the right during the slide, get past the first "stop" platform reachable by a steam geyser (where a fairy can be found), then head to the next stop platform and stay there. (If you missed it: move on, jump ahead twice, go right and jump into the huge steam geyser.) Look left: there are two steam geysers. When both of them are activated, rush towards them to glide in two steps towards the platform upward. Dig the ground to find the fourth Piece of the Key! Then jump down and slide until the end of the slope.
Go ahead, jump towards the skulls, then jump to the right. Pick up the Bomb Flower and throw it on your left, where some boulders are preventing the lava from flowing. Part of the ground is now freed. Pick up another Bomb Flower and make it roll towards the huge boulders on the other side. Go there and dig the ground to find the fifth and last Piece of the Key and re-form the Earth Temple Key! Get out, jump on the small platform, then jump to the right. Get in the cave and jump into the huge steam geyser to climb back up into the building. Cross the bridge and get back to the Bird Statue, then get close to the great door and open it using the key.