1. Grab the medkit before dropping through the opening in the floor.

2. You'll land on a grate which will break open, allowing you to fall to this underground area (note the red grate). You can drop to the ground below or remain on the catwalks, it doesn't really matter. Take down this initial opponent seen here.

3. If you drop below you'll find a medium medkit here.

4. Advance to battle this ninja-like warrior on the right.

5. You'll also have this ninja to contend with below-left. Continue left to the end of the catwalk visible ahead.

6. Peer through the boards and take down two more ninjas. This area is your ultimate destination.

7. You can't get through the boards so we'll have to take the long way around. Head right and this ninja pops up from around the corner.

8. Around the next corner you'll have more ninjas, above and below.

9. Advance across this beam. If you've already dropped below, use the rotating sign as reference.

10. Advance ahead and you'll come under fire from a ninja above the red sign, a second below the red sign, plus a third to the right.

11. As if that isn't bad enough, you'll have these three respawn behind you.

12. Drop below if you haven't already and finish off this final ninja of the area. Search for health and ammo before continuing.

13. Climb through this opening on the right. Note the boarded-up fence on the left that we had fired through earlier.

14. Battle this trio of ninjas then ascend these stairs.

15. A fourth will spawn above. Here he is dropping an armor vest.

16. Two more ninjas up ahead. This one above and another below. Advance across the left board -- the right one is unstable.

17. Here's a shot of some serious ninja jumping action. Follow the left ledge to the large pipe ahead.

18. A hole in the fence will allow passage to the other side, but you want to be on the pipe to drop over this fence up ahead.

19. This area is tough. Clear out as many ninjas as you can before ascending those stairs.

20. There are more ninjas behind those pipes, plus another behind the fence far-left. You don't have to deal with them, though -- just make a mad dash for that door straight ahead to load the next level.