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Playstation 2 - Return to Castle Wolfenstein cheats

Unlock the original Wolfenstein 3D.
Finish the single player campaign mode

Peeking around corners
Click and hold the Left Analog-stick while moving it right or left.
Note: You cannot shoot.

Bonus armor, health and ammo:
Find all the secret areas in any given level.

Head shots:
If you turn off the automatic aim option, you can shot the enemies to head shot. 

Extra stuff:
Perform a stealth kill, and you will get all items which dropped by the enemy