This Artifact is found in Chapter 16 - Prison of the Damned (2). After the cutscene where Kratos kicks Tisiphone off of the cliff, go back to the door you used to enter the area. If you go through the open doorway, you'll fight an Empusa, so go back after killing it. It's on the ground to the right of the Green/Blue Chests.
When activated, your health will slowly regenerate.
