Potamos Hideout
This is the hideout you'll clear in the course of The Hungry River side quest, tucked away in a little canyon.
You'll note that some of the enemies have the specific status of 'Ambushing,' meaning they're reading to attack anything that comes in the canyon way. You can easily evade them from attacking up top, or snipe them- they're too far from camp to raise a ruckus. Sniping, in fact, is good way to deal with almost everyone here (there is an arrow cache down below for reloading).
Your two primary targets are the captain, and whoever's guarding the treasure this shift.
Snipe anyone else between you and the loot, then drop down to the wooden bridge and get some more arrows. Drop down to the lowest level to loot the red chest, and complete the location.