This achievement is unlocked when you find this artifact:
#45 Bird - 31:03
Towards the end of the game, you'll find seven tall guards standing in front of a town. To the right of the guards is a small house with a strange bird spirit inside. You'll need your mask to see the spirit. Turn on your light and lure the spirit out of the house, to the left, toward the guards. When it gets close enough, the guards will kill the spirit, reveal an artifact, and unlock the achievement.