After you’ve used the lift’s lever, you’ll find yourself in the northern part of Blackreach and the Greymoor Cavern Great Lift. Head north and find the Greymoor Keep Wayshrine. The outer keep walls mentioned in the shard’s title are the first line of defense of this, the largest and northernmost structure in Blackreach. Our final goal is a part of the outer wall with a lava pool next to it. There are four of these pools close to the outer wall, and the one we’re aiming for is the easternmost one.
From the Greymoor Keep Wayshrine, continue north toward the keep. Try avoiding getting close to the closest pond, as it’s a long way down from there, and you might not survive the fall. Find a path that leads downhill and you’ll be fine. Follow the path to the northeast, past two large stone towers. As you get close to the easternmost lava pool, you’ll notice there is a large gap between the platforms on the opposite side. The monsters here like to slow their targets down with their first attack, so keep that in mind when trying to jump over the lava gap. I’ve made the jump near the gap’s western part, and even with the slowdown, it barely took me over. From this platform next to the outer wall, head north, and soon enough you’ll spot the skyshard’s location.