Here's a full video walkthrough of how to do Act 1, with three other achievements you'll find in the act, including this one (and it's timestamped).
During this act, you'll enter the mines. In the mines, you'll move to the far right on a track. When you go to leave, you'll get some dialogue. May sure to press "If you wait for me here, I'll just go take another look around."
Shannon will go back in the mine. I had to walk far to the right to be able to turn Shannon, to the point where she is directly facing the player (you). When in the right spot, the light flicks, changes colour, and different music comes on. Then after it gets more intense, turn away, unlocking the achievement.