Press B, Y, Right, Left, Right, Left at the "Access Denied" screen that appears after you complete a level without collecting all cages and lums. The word "Cheat" will appear under the "Access Denied" message to confirm correct code entry.
Tomb Of The Ancients: Hidden area
Reach the last area in the Tomb Of The Ancients level. Get on the dark spot on the third panel behind the "Technical Check-Up" door, then press B, Y, Right, Left, Right, Left. A crate will appear will confirm correct code entry. It will allows you to access a hole in the wall. Once inside you can view various secrets about the game.
The Crow's Nest: Unlimited ammunition
Fly towards the highest point of the roof in the level and keep trying to hit the center. Hold B + Y until you hit it. If done correctly, you will teleport into a metal pipe structure. Reach the end of this structure and you will teleport back to the main area. The orange balls of ammunition that normally appear will now be blue, and will never run out unless you get hit.
Strategy guides from GameFAQs