Hide and Squeak
This first bonus mission is unlocked during the main game mission "Find Susan's Horn." As soon as the timer reaches zero in this mission, move to the left-hand side of the screen and repair the lock on the bonus chest. Open this chest to unlock "Hide and Squeak." This bonus mission involves using brothers Edmund and Peter to work together and rescue some Narnia creatures from a perilous cliff.
Beachside Brawl
To unlock the "Beachside Brawl" bonus level, enter the "Break into Miraz's Chambers" mission and find the three yellow puzzle pieces. Simply collect them all and fit them together in the nearby wall mount. This bonus level requires you to survive a two-minute ambush of Telmarine enemies in which you must attack and defend simultaneously. If you can make it to the end of the two minutes, you'll be rewarded with a bonus video.
Giant-Sized Fun
The bonus level "Giant-Sized Fun" is unlocked in the middle of the level "Defeat the Sentries." Right before the crest puzzle, climb the tower all the way to the top. The chest here is difficult to spot unless you're looking for it -- open this to unlock the level. "Giant-Sized Fun" is tailored to two players -- giving you and a partner control of a pair of powerful minotaurs. Your goal is to defeat 99 Telmarines in under two minutes.
Plunder Pressure
This final bonus level is unlocked at the tail end of the mission "Find a Way to the Cistern." As you approach the final exit door, take note of the spinning lion head above the door frame. Shoot at this icon to unlock the "Plunder Pressure" bonus level, in which you must attempt to open a damaged treasure chest while under waves of attack from the Telmarines.