Darston hasn't returned from investigating the strange sounds coming from Eldin Volcano, and the elders ask you to search for him.
Where to Start the Quest
After you complete the quest The Rift on Eldin Volcano, go into Goron City and talk to Gol to start the quest.
How to Complete the Quest
North of the Lizalfos Burrow, there is a cave on a cliff called Summit Cave. Go inside and you find Darston. Go up to him and there will be a cutscene.
Afterward, go north through the door. Go north and move the lava rock onto the lava spout, and jump onto it to go up to the cliff. Go south to the rock wall and climb on it to reach the lava rock on the spout. Then climb on the next section of the rock wall and create a lava rock on top of the next spout. Ride it up to the cliff.
Get on the lava rock to the north, then make another lava rock on the spout to the north, to reach the ledge north of that. Then instead of making a lava rock on the spout to the east, make a regular Keese and glide to the lava rock to the southwest. Then hold Y to make a lava rock on the northeast lava spout. Glide there when your lava rock goes to the top. From there, jump east to the ledge, and go through the north door.
The Fire Keese in this room will set the grass on fire. If you have a Chilly Potion or other drink that makes you flame-proof, you can use it here to go through the room more easily, but be aware that you can't walk through burning grass. It won't burn you, but it will push you back. Reach the northeast part of the room and climb up the rock wall there.
Create a lava rock on the nearby lava spout, then bind to the lava rock in the northeast part of the lava lake, and pull it south. Move it onto the northwest lava spout. Then create a Keese and pick it up, and glide from the nearest lava rock to the northwest lava rock. Go north from there and down the ladder.
As the lava level goes down, climb down the ladder. After you jump over the first gap, create a lava rock or cloud or other echo to go past the larger gap. Climb up the rock wall, defeat the Torch Slug, and open the chest to get 50 rupees. Wait for the lava to go back down, then climb down and go to the right, and go up the next ladders. When the lava goes down again, climb down the ladder, go to the right edge of the ledge, and hold Y to make a Strandtula. Then make echoes so you can reach the Strandtula. Climb up its thread to reach the ladder. Go up.
Go through the north door.
Fire Talus
Now you must battle a burning Talus. The strategy is similar to the Seismic Talus, but the flames make it harder to pull on the glowing orb. Use echoes to distract the flame Talus so it attacks your echoes instead of you. This gives you a chance to run behind it or to the side of it to more easily pull on the glowing orb. You can also shoot the orb with arrows.
Quest Reward
You get a Piece of Heart when you defeat the fire Talus. Go back and talk to Darston, and he gives you a Goron's Bracelet, which lets you carry things more quickly when you equip it.