In Celyon, 2nd level (hunters camp) when you drop the box off the ledge that is tied by rope, there is an artifact in there.
Artifact locations at Ceylon
Artifact - Location
Idol Of Ramba Vihara - Gates Of The Lost City
Mahavatu Mask - The Hunter's camp
Port Negombo Relic - The Palace Of Forgotten Kings
Avoid falling damage
Press R as before you hit the ground to enter combat mode. You will not get any damage from falling.
Drink from canteen
To drink from the canteen, hold A. If you instead tap A, it will take longer. Holding A also helps when you fill your canteen.
First Artifact
On the first level go to the water fall and go behind it and you will find the first artifact of the game.
God Mode
Hold L + R and press Up(2), Down, Up, A, X, A, B, Up, Down, Y, Start at the "Press Start" screen. Note: Use the D-pad. A song will confirm correct code entry. You will become invincible with unlimited ammunition.
Jump from any height
Go into combat mode before you hit the ground and you can jump from any height without hurting yourself.
Missing hat
Pause game play and look carefully at Indy to notice that his hat is gone. Look at his forehead during game play, then and look back at his forehead.
Panzershreck
When you start Peng Lai Lagoon: The Secrets of Peng Lai Lagoon Part 2, go straight forward until you're stopped by a wall, then go to right corner of the wall. There you'll find a DEMO-CHARGE, if you don't find it, move your camera around. Pick up the Demo-Charge, then point yourself to the other corner, and if you look diagonally to the left, you'll see a wall with a crack, go and place your Demo-Charge there. Run away so that you're not damaged by the explosion. When the wall has been blown up, walk trough the hole, and pick up everything in the room. You will find the Panzershreck+Ammo and an Artifact. Just so you know, you can't destroy the big vase in the middle of the room. If you pick up something else, go swimming or use something else, you'll drop it. This weapon is more fun with the God Mode cheat, because then you fire how many missiles you want.
Pistol whip
Press X button to pistol whip your adversary. Note: This works for all guns, not just the pistols.
Skip all poachers
In the level where you start out in a room enclosed by a vine door, cut the door and walk forward. It should start a short intermission sequence of Indy running towards a little window. Skip through it and when it is over, select the whip and jump. While in the air press A. If done correctly, you should now be swinging above a courtyard. Swing to the other side and continue the mission.
Unlock Art Gallery
To unlock the Art Gallery, find all of the artifacts in the game.