The 'Hall of the Mountain King' is from the Peer Gynt suite by Edvard Grieg. It tells a story of Peer Gynt's adventure in the mountain. He enters the hall of the Mountain King, where the atmosphere is spooky and full of mystery. The music that represents this part is very famous, with a gradually intensifying tempo, creating a sense of unease and the approaching of something powerful.
Well, in the 'Hall of the Mountain King' story, Peer Gynt is a rather complex character. He wanders into the Mountain King's domain. The Mountain King has his own little world there. As Peer Gynt moves through this hall, there are all sorts of strange creatures and an overall sense of the unknown. The music really helps bring out the story, making you feel like you're right there with Peer Gynt, experiencing the strange and somewhat intimidating environment of the hall.