For this achievement you simply need to roam around Cold Run until you have 'discovered' all of its zones/areas. These include the following: Calder's Creek, Dead Man's Point, Gulbrand's Gorge, Hakon's Fjord, Lone Man Overlook, Ragna's Ridge, Roald's Bluff, Storvald's Breach, The Bitter Shore, and Valley of the Frostworm. Here is a screen of my map when the achievement unlocked: