At the Options menu go to Cheats then enter the following codes for the corresponding effect.
Unlock God Mode:
Vitruvian Man
Unlock Level Select:
Clos Luce 1519
Unlock ALL Bonuses:
Et In Arcadia Ego
Unlock Double Health:
Sacred Feminine
Unlock One Hit Fist Kill:
Phillips Exeter
Unlock One Hit Weapon Kill:
Royal Holloway
Unlock ALL Visual Database Entries:
Apocrypha:
Unlockable Secret Levels:
To unlock Rosslyn Chapel Revisited and The Louvre Revisited you must complete the game.
