You should have the night vision goggles turned on all the time, even when you're closer to bright spots. As for the level itself, it's not that hard, mainly because it's rather straightforward. You will have to reach the opposite end of the cave complex. You will be encountering some enemy forces along the way (#1). Thankfully, with the night vision turned on you won't have any problems locating the terrorists. Nevertheless, you should be very careful. Slow down a little once you've reached the main cave (#2). Before entering this area make sure you've reloaded your weapon.
You should see a group of enemy soldiers. Most of them will be stationed on the other end of this cave (#1). Use the fact that they can't hurt you, mainly because they're equipped with lame automatic weapons. Nevertheless, you should be careful. Some of the terrorists will attack you from the right flank. Once they're gone, head on to the only possible corridor. You will be encountering enemy forces quite regularly (#2).
The second important location is the wooden bridge area (#1). First of all, take care of all nearby soldiers. Most of them will be hiding on the left side of the bridge. Make sure there's one left alive. Cross the bridge and keep moving forward. You should be able to reach the exit within a few seconds (#2). I have to warn you, though. This area will be guarded by at least two additional terrorists. Kill them. Get closer to the ladder and wait for the game to load the new level.