The Thunderhead is a location from The Legend of Zelda: Skyward Sword. Found within a mass of thick clouds in The Sky, the Thunderhead is a collection of floating islands centered around a thunder and lightning theme. It is here that Levias can be found.
After Link plays the "Ballad of the Goddess" atop the Light Tower, a beam of light is shot into the Thunderhead, creating an opening into the otherwise impenetrable mass of clouds. It is here that Link finds the Isle of Songs, where he returns multiple times to learn "Farore's Courage", "Nayru's Wisdom", and "Din's Power".
Later, on his search for the Triforce, Link brings Pumpkin Soup from Pumm as an offering to the spirit of the skies, Levias, in order to enlist his aid. However, the spirit has been infected by a parasite known as Bilocyte, forcing Link to battle him. Following Bilocyte's defeat, Levias is freed from its influence and tells Link of the "Song of the Hero" and to seek out its three parts from the Three Dragons on the Surface. Defeating the parasite also leads to an improvement of the weather inside the Thunderhead.
After learning the three parts of the Song of the Hero, Link returns to Levias in order to learn the fourth and final portion of the song. Levias then encourages Link to return to Skyloft in order to uncover the final resting place of the Triforce.
One of the islands inside the Thunderhead also serves as the location of the Bug Heaven minigame run by Stritch. Here, Link can catch different types of bugs for various rewards, and must do so at one point in order to reclaim Beedle's lost Horned Colossus Beetle.