In the heart of the world, during the video with the teensie king you will notice one of the pillars has a ledge on it. Climb up it once the video has ended and walk to the left until Rayman stands on abutton and says "Hoooyeah, yaha" or something like it. A door will open and if you go in there will be a sort of spirally slide thing that has lots of jewels going down it.