This achievement can be done in the Geothermal Valley
from the Ruins Encampment
Base Camp. From this base, run up the hill and spot the dome shaped building near the top of the hill. You'll need to access this area by going up the hill entering the building next door 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 left to find a small wooden chair on a small piece of the roof. Pull yourself up, approach the chair and press
to sit down, unlock the achievement.