Very nice little game. Good work on the game and the amazing manual (that I gave a speedy read).
Didn't find the artifact but I thought the last three doors when unlocked will going to give some keys.
Thank you for trying both the game and the manual out! Unfortunately, those last three locks are just plain old locks, but you were pretty close to the artifact...!
A day later I had 11 keys in the last room. I got the artifact =). Again, amazing game.