1. Hop through this hole in the wall.
2. Continue through the indicated shaft. The door to the right leads to nothing but trouble - three rocket-launching guards and no booty. Avoid it.
3. Take out the opposition before dropping below.
4. Hug the right wall to avoid falling into the chasm. Enter the indicated room to find a large medkit and three grenades. If you're itching for a fight you can continue downstairs, otherwise continue through the door straight ahead.
5. To the left is a sealed cavern. You want to head right and help your comrades in this battle.
6. Pick up a medkit and armor vest here.
7. Climb this fallen vent to the indicated opening.
8. Next up is a nasty battle against a number of RPG-wielding enemies, including these two exoskeletons.
9. Activate this panel seen on the right then jump through the opening that appears on the left.
10. Continue through the opening where this explosion is seen here.
11. Enter the doorway at (1) then descend the stairs and hop into a neighboring room to emerge on the other side of the partition at (2).
12. Ascend through here.
13. Save your game before approaching this gate -- it's about to fall and you are about to be ambushed.
14. These bombs drop from the ceiling. You can hear their beeps counting down to an explosion.
15. Quickly make your way to this elevator at the opposite end of the hallway, to the left. You can safely wait out the explosion in here. You don't have to close the door but you can if you like.
16. Return through the gate that closed on you before, then continue to this battle. These guys are deadly accurate with their RPGs and are not very vulnerable to yours. I recommend primary fire as seen here.
17. Once the area is secured, slip under this door.
18. This is a very easy jumping puzzle. Just keep the distances small as you take short hops to the bottom.
19. Climb through here.
20. Help your buddies in battle then continue through this tunnel.
21. Ascend the stairs then go through that door ahead.
22. Here I am being killed by the welcoming committee on the other side. I actually found it best to snipe them from just outside the doorway.
23. If you proceed straight ahead you'll be mowed down by automatic turrets. Instead, defeat two guards on this bridge above then head through the indicated doorway.
24. Climb a ladder and these stairs to defeat two more guards above.
25. You'll have a better angle on the turrets (and guards) from up here. Hop below, using the green machine seen on the left to break your fall.
26. Destroy this turret.
27. Slip under the partially-opened door behind this drilling machine. Note the large medkit to the left.
28. Take out two exoskeletons.
29. Snipe this exoskeleton before descending the ladder seen at the bottom of the scope.
30. This vehicle powers up. Take out these two guards, plus a third to the rear.
31. Climb the opposite ladder then take down this exoskeleton. Two large medkits are around the corner on the right.
32. Follow that jutting rubble to the rocky ledge.
33. Guards pursue through the door next to the explosion. Continue through the doorway on the right. (Note: If you are having difficulty making the jump, follow this tip from Gary: "You have to stand in the corner then do a jump + crouch quickly. I found when I did the jump + crouch at the same while walking forward it worked.")
34. Defeat these two then pass through a door on the right.
35. Use Adrenaline Mode and your sniper rifle to take out the guards below.
36. You'll also have these two guards to contend with as well.
37. Fight your way down these stairs and across the catwalk.
38. Grab this large medkit before carefully descending those stairs.
39. Avoid the hole at the bottom of the stairs. Continue through the open doorway.
40. Ramp down this fallen air shaft. (Defeat or ignore the turret to the right.) Ascend those stairs ahead.
41. Proceed through the indicated opening.
42. Make your way through the tunnel, continuing past the drilling machine as indicated.
43. Carefully step across the chasm to the doorway straight ahead.
44. Jump-crouch to the ledge above as indicated.
45. The tunnel caves in behind you. Drop through a hole behind these ventilation units.
46. You're now in a maze. Watch your back as enemies spawn behind you. Fortunately, many medkits can be found in this area.
47. You're almost out when you see the stain to the right. Continue as indicated.
48. Bear right as indicated.
49. To the back-left is this opening, only visible once you are upon it. Pass through the opening to trigger a cutscene and load the next level.