To unlock this achievement, you need to deactivate the 9th orb. To find it quickly, load the 44th checkpoint (when you are chased by the underwater long-haired creature). First, you need to push the red button underwater to bait the creature on the right side of the room. Then, dive back underwater on the left side of the room to reach a secret area where the orb is (watch the video below):
Respite achievement:Full walkthrough of the game: