Rolling Green Galaxy is a galaxy in Super Mario Galaxy. It vastly resembles a golf-course, and in it, Mario balances on a large ball, and needs to maneuver the ball through the galaxy in order to locate the hole that will open it. Doing so will enable him to receive the Star. To keep the ball stationary, the player will need to keep the Wii Remote up; tilting it any direction will result in the player moving in that direction.
The music here is the same music that plays in the obstacle course levels of Super Mario Bros. 3.