Now return to the large building. Move under the opening in the front, to the left of the flaming barrel where you shot the guy with the explosives.
From here you can target another welder working inside on the right. Again, a silent headshot with the bow is the way to go.
Climb into the opening and pick up 2 bunches of arrows, one on each side. Then go through the doorway into the stairwell and loot the welder's body.
Climb the stairs to the upper floor. Shadows on the wall reveal the presence of at least two more solders up here, so go carefully.
If you did not shoot the man operating the spotlight from down below, he'll still be here now. So move carefully to the top of the stairs...
...and take him out with a headshot through one of the holes in the wall.
Step through the doorway and immediately turn left. Stay close to the wall, since there's another enemy just ahead.
Hide behind the desk and take him out with another silent headshot.