Assuming you enter this route from the left, your first challenge will be to get over the pit. You can shoot the flame which flies upward twice to remove it. Then jump from the low ledge on the left up to the high one. Let it sink a little before making the jump to the high ledge on the right, and then down to the other side. If you fall in the pit, simply swim to the right, exit the cavern, and try again.
Shoot any of the enemies that occupy the screen to the right (you won't see most of them unless you drop back down from the screen above) and then jump up through the gap in the ceiling to the next part of the route. Slowly falling enemies will hover in the air above when you arrive. Navigate yourself to the top of the ledge, removing these enemies when you can. Then proceed to the right.
Heat seeking missiles will begin to appear as you approach the wall with the narrow gap. You'll need to squat down and crawl in order to get through the wall. Fire continuously to the right to destroy all of the heat seeking missiles that show up. Then proceed to the exit on the right.
