Press Select, Square(2), Circle(2), Triangle, Square, Triangle, Circle at the main menu. A cheat menu with "Invisible" and "Silent" options will be unlocked. Turn them on and enemies will not see or hear you. Select "Continue" to access a level selection screen. Press Left or Right to choose between levels.

Cheat Menu

• At the main menu, press Select, Square, Square, Circle, Circle, Triangle, Square, Triangle and Circle to bring up a cheat menu
  
  Pro Action Replay Cheats
  
  (M)
  0E3C7DF2 1853E59E
  EE8EF392 BCA99C80
  
  Inf Health Largo Jack's Place
  C1A99FCA BCA99E6A
  
  Inf Health Largo Vorograd
  C1A96836 BCA99E6A
  
  Inf Health Simon Vorograd
  C1A96832 BCA99E6A
  
  Inf Health Largo Monastary
  C193C07A BCA99E6A
  
  Inf Health Joy Monastary
  C193C006 BCA99E6A
  
  Inf Health Largo W-Food
  C1A67DF6 BCA99E6A