Defeat the Mongols
Head along the west coast to the south of Sago Mill and you’ll come across a checkpoint in the middle of the road, Frozen Overlook, a small Outpost.
As with all small Outposts, the main objective here is to defeat all the Mongols and it’s a good idea to approach from the western ridge as it gives you a great look over both parts of the Outpost. As you’ll notice, there is two levels here and you’ll want to go about clearing the upper level first, taking care of the lone archer on the ridge to begin with. There are five more Mongols just below you, along with a Dog so consider a Chain Assassination or even a Standoff. Another group awaits you below and if you were fortunate enough to not alert them, begin with a Chain Assassination once again. Once the Outpost is clear of enemies, be sure to pocket the Mongol Artefact on your way out.