Liberator Achievement

Outposts are marked on your map with a black flag and Eden's Gate seal in the middle. To liberate one, you'll need to kill all Cult guards within it. Once the Outpost is cleared, the area will be liberated and become populated with civilians, which will open you up to new shops and quests.

Take your time when taking on an Outpost and make sure you do not get caught. If you get spotted, the guards will sound the alarm and backup will arrive. So make sure you take the stealth route by marking all guards with your binoculars and disabling any alarms up close or shooting them.