Bowling
Hit every panel in the credits. At the end, along with earning the 'Developer smash' achievement, the player will continue into the bowling area.
Don't worry about breaking everything
As you work through a course, you may be tempted to try and remove all barriers. However, you don't score any extra points for doing so, and it can waste balls that you'll need to survive your attempts at the more difficult areas you'll encounter later in the game. Instead of trying to clear a wide swath, focus only on those obstacles you absolutely need to clear. For instance, don't try to eliminate an entire wall, which can cost numerous balls. Instead, try to carve a path through the middle. You'll be grateful that you showed restraint once the game presents you with more challenging obstacles in the late going.