Fast travel to the Ruins Encampment Base Camp in Geothermal Valley. From this base, run up the hill to see the dome shaped building near the top of the hill. You can access this area by going up the hill, entering the building next to it, and using the tree branch to swing across. Once you swing across into the tall domed building, hang off the ledge and shimmy to the right to find a wooden chair on a small piece of the roof. Pull yourself up, approach the chair, and press X to sit down to get the "Quiet Time" achievement.