During gameplay, press TAB then type in these codes:

GOD - God mode
ALLAMMO - Full ammo for all your guns
FLY - Fly mode
GHOST - Walk through walls
WALK - Return to normal mode
PLAYERSONLY - Time freeze toggle
OPEN [mapname] - Warp to any map
BEHINDVIEW 1 - Tomb Raider view on
BEHINDVIEW 0 - Tomb Raider view on
FLUSH - Fix bad textures on walls or creatures
INVISIBLE - Become invisible KILLPAWNS Kill all monsters 
SUMMON [object] - Summon weapon, item or monster 
SLOMO [number] - Change speed of game - 1.0 is normal.