After Faron and Eldin, only Lanayru is left, but where to go? The three dragons... who told you about them? Of course!
Lanayru Cave
Fly to the Ancient Harbour in the Sand Sea (or Lanayru Desert - west) and get back into the cave where the old Goron told you about the dragons' legend. Talk to him, he's very interested in the sacred flames and tells you that he pursued his researches. He found a narrow passage and thinks that there must be another region further, but also that the Thunder Dragon and robots are linked. Make a bomb roll into the passage to its right, go ahead crawling and get into the...
Lanayru Gorge
After Fi's information on this place, take a look at the Bird Statue to the right and notice the big skull to the far south (opposite where you came from). Go back to the statue, launch the Beetle at the cactus so it grabs the Bomb Flower and drop it on the rock on the pillar. Then jump towards this pillar, and further, and read the stele that says that the entrance is forbidden without the Thunder Dragon's approval. Go to the end of this path towards the round rock and take a look around: Something is shining atop one of the pillars. Send the Beetle in this direction and pick up a Small Key! Get back in front of the door and unlock it.
Go ahead, shoot the Clawshots at the Peahat, then the following one, the target, and finally get into the corridor. Take a look at the Timeshift Stone in the cart and use your thrusting strike to bring the cave back to life. Now speak with the small robot looking for huge Timeshift Stones to offer to the Thunder Dragon.
The cart will then start to move, follow it and step on the switch to open the door. Get rid of the enemies or avoid them, then step on another switch. Go on following the cart, walk on the temporary path, clear out the Technoblins, then grab the vines, let go on the switch and go ahead. Now jump onto the temporary path, go left, then grab the vines on the left and let go on the slabs. Go towards the other side of the corridor, jump towards the platform with the Deku Baba, attack it, then grab the vines on the other side, let go and step on the switch. Use your Clawshots again on the vines ahead, go left while picking up the Stamina Fruits, and jump left when the wind isn't blowing. Go down on the slabs when you can see them. Then shoot the Clawshots at the target on the other side, then at the one behind you, let go and step on the switch. Next, use the Clawshots at several targets on both sides of the corridor as soon as they become "grabable", then finally at the vines and go on.
Get rid of the Chuchus and Deku Baba, then upon reaching the bars, throw the Whip at the lever and pull to lower it. Beware the Chuchus, the spike traps, strike another Technoblin, then throw the Whip at the hook to get across. Cross another gap, avoid the spike traps, go ahead, then climb the small slope to the right and lower the lever. In the next room, get rid or avoid the Chuchus, Technoblins, Sentrobes and the three Beamos, but one of the latter is blocking the track thus you must destroy it! Next lower the lever using your Whip and keep on following the cart. Walk on the temporary path, clear out the Deku Baba, then launch the Beetle at the bomb behind the cart to destroy the rock blocking the track. Fight or avoid the two Deku Baba, then a Quadribaba, and the cart will reach its final destination! All the area is brought back to life and the Thunder Dragon appears!
Talk to the small robot that informs you that the dragon's life is endangered. Speak to the obviously ill Thunder Dragon, but since he is ill he can't help you and can't sing. Talk to him again to learn that the robots tried to plant a seedling from the Tree of Life, whose fruits can cure all diseases. Then talk to the small robot northeast that informs you that they planted a seedling behind it. Follow this path, use the Gust Bellows to go ahead (and find some ants), then cross the sand to the desiccated tree. Vacuum the sand, hit the Timeshift Stone, then talk to the robot there that tells you the tree has trouble to grow there. Dig near the seedling to gather the Life Tree Seedling, then get back to the Bird Statue (by launching the Beetle at the Timeshift Stone in the cart) and take off to the...
Sealed Grounds
... because you remember Groose's wish! Get in the temple, talk to Groose, then plant the Seedling into the small hole. But Groose tells you that it will take ages to get a tree. Take back your seed and open the Gate of Time. Plant the seed at the same place, then go back to your era: A wonderful tree has grown! Send the Beetle at the fruit to make it fall and pick up the Life Tree Fruit that can cure any illness! Leave the temple to get back to...
Lanayru Gorge
Speak with the Thunder Dragon and throw the huge fruit at it! Immediate effects! The dragon will thank you and teach you his part of the Song of the Hero. You learned another part of the Song of the Hero! thanks to the wonderful tenor voice of the Thunder Dragon. To thank you, he will prepare a surprise for you...
Fi congratulates you for finding the first three melodies and advises you to visit Levias again. Take off once more to the...
Thunderhead
Fly to the wise Levias, jump on his head and he begins to sing the last part of the song. Then, the three dragons join him to sing each part of their melody while Fi is dancing. You reformed the Song of the Hero! This song will reveal the entrance of the next trial and once you've succeeded this trial, the path to the Triforce will open. Fi adds that the trial is located on an island in the sky and that you can use your Dowse ability to find it.
Use your dowsing to see that this island is towards the entrance of the Thunderhead, and in fact outside of the Thunderhead and it is...
Skyloft
Still using your Dowse ability, go to the plaza located south of the island, notice the butterflies and play your Harp. As usual play along the rhythm to make a rosette appear and Fi informs you that you got into the Goddess Silent Realm. Once the Spiritual Vessel is filled and the trial completed, the door leading to the Triforce will be revealed. During this trial, you have to really pay attention to the lantern carriers and the guardians, as well as not going too fast! Run straight ahead and pick up the first Sacred Tear. Pick up a Light Fruit a little further, then run left and take the Dusk Relic in front of the windmill. Go on towards the school, climb the stairs, climb on the two crates to the right, pick up the fruit, then jump to the other side. Grab the ledge on the left, go left, let go near the fruit that you can pick up, then go to the vines, climb and pick up the second tear on the roof while avoiding the lantern carrier to the left. Then jump down between the two light fences, push/pull the crate in several steps to stay out of the light, then climb on the crate to get the third tear. Go east, pick up the fourth tear at the top of the stairs, then walk them down and go left. Pick up the fifth tear southeast of the Bazaar, then go on, pick up a fruit, then the sixth tear in front of the bench (and next to the guardian) ***. Go ahead a little, stand on top of a small staircase to avoid the lantern's light, then pick up the seventh tear at the end of the pier.
Go down the small staircase, follow the path north by walking on a small wooden part (safer), then go towards the small windmill and jump lower at this place. Pick up the eighth tear to the north (next to the flat rocks on the lake), then go left and - when the lantern carrier gets away -, get on the planks, then on the narrow plank where the ninth tear is. Get back right when the way is clear, then jump on the rocks in the lake and pick up the tenth tear a little further. Cross the rocks again, go south (while staying left under the small pier), then, when the lantern carrier to the left is getting away, cross the bridge while picking up the eleventh tear on the way, then run to the path going up. Go left, pick up carefully the twelfth tear in the middle of the four lantern carriers, then take the path going up southwards, pick up the Dusk Relic in front of the windmill, then jump down next to the thirteenth tear and pick it up. When the Revealing Water leaves the path, run, then climb the path going over the house (safer), jump to the right towards the back of the graveyard and pick up the fourteenth tear behind the tombstones. Only one left! Climb the stairs while staying on the right to leave the graveyard, go right, then cross the bridge again but close to the end jump left, onto the river bank to avoid the lantern carrier. Run towards the Light Tower, then be careful with the lantern carrier going around it and climb the two ladders to pick up the fifteenth tear at the top! Jump to the bottom of the tower and get back in the rosette to complete the trial. You get the Stone of Trials!
Check the Skyloft map with the 15 tears
*** If you have trouble completing this trial, especially close to the end, a solution is to not pick up the sixth tear which is easy to get and close to the start, and to keep it for the end in case you would get spotted by the guardians or the lantern carriers.
Fi will congratulate you, then say that the Stone of Trials is part of a two stones set, and that you can find another identical red stone somewhere on this island. If you are a good spotter, you already know where it is! Head north, jump on the flat rocks, then go left and take a look at the Bird Statue with a unique red eye... Examine it to place the Stone of Trials, then the statue will rotate and shoot a boulder at the part of the island where the Goddess Statue is. The statue will crumble down a little, then the rocky part at the bottom will fall to reveal a door! Fi announces that your last quest is close! If you have about twenty arrows and bombs, along with at least a potion or a fairy, shoot the Clawshots at the targets to reach the door and get inside...