Hollow is the second floor of Jungle Island in Super Monkey Ball 2 (19th in Super Monkey Ball Deluxe), the second floor of Beginner in Super Monkey Ball 2'sChallenge Mode, and the second floor of Ultimate in Super Monkey Ball Deluxe's Challenge Mode.
The only goal in this level is a Blue Goal.
The Blue Goal is considered easy to reach. Turn left after rolling off the starting platform, and follow the curved path of the stage. When you reach the wall, turn right, and roll into the goal.
If you want a good score, jump the corner of the first wall at a fast speed, bringing you to the center and possibly earning a Banana Bunch. However, unless this is done exactly right, you can easily miss the center and fall out.