Fade to Silence

Depending on which direction you decide to head once you reach The Flats, this achievement can come very early on in the game. Once you reach The Flats head East and slightly North, on the map you'll see a dotted line which separates The Peaks from The Flats.

The achievement popped as I crossed that dotted line.

If you are playing co-op, this achievement is host only.

For anyone who plays this on coop, the person that joins the host will not get the achievement for discovering the Peaks when found.