1. Start by climbing this long ladder.
2. Take out as many guards as you can before dropping to the catwalk below. Descend a ladder to the right.
3. Jump onto the concrete rubble on the right then leap to the indicated vent. If you cause the elevator to fall you can climb the ladder back up to this position. There isn't anything inside the elevator so your best to just avoid it.
4. Scurry along this beam to the ladder far-right and climb down. Guards will start firing at you from behind the grate on the left, so move fast.
5. This elevator drops to the bottom of the shaft. Hop down to the roof of the elevator and exit as indicated.
6. Grab this small medkit and the Taff 20-4.
7. Climb those barrels to reach the vent above.
8. You've just emerged from the opening on the left. Drop as indicated to the ladder below.
9. Descend the ladder to this position, drop to the catwalk ahead and enter the opening on the other side.
10. Crawl to this neighboring shaft, where a bridge-like piece of rubble drops into place, allowing access to the ladder far-left.
11. Descend the ladder then climb into the indicated vent.
12. Climb out onto this plank then leap to the ladder far-left.
13. Descend all the way to the bottom, then climb the ladder seen ahead to exit out that door and load the next level.