(1) This is one of the more varied and interesting levels in the game. As soon as you open the entrance door, you will be beset upon by 2 or 3 facehuggers. I like to back up and kill them inside the entrance lock so that I don't have to deal with them later. You will have to move forward to activate the 1 or 2 remaining 'huggers ahead before backing into the airlock to dispatch them. Watch your fire near the entrance; hit the left wall and you will blow 1 or 2 steam jets, one of which is unavoidable! Now move ahead and turn around, since a warrior will be arriving shortly to make life difficult for you. Express him to the hereafter with a grenade.
(2) Now blow the 3 crates blocking the short stairway near the entrance (you'll get a seismic charge for your trouble) and go up. A carefully-timed run gets you past the steam discharge (there's a med kit here, too).
(3) Pulse-rifle the 2 facehuggers dead ahead so you can grab the auto-map, battery, and pair of derm patches. While up on this platform, try to stay to the left side or you may activate some eggs below. You may also have a warrior (or 2) come up after you from a lower part of the level; grenade 'em.
(4) Now go back down the stairs (once again deftly avoiding the steam jet) and turn right. Blow the 3 crates ahead and earn 6 derm patches. As you near the room ahead, face left and sidestep in; a company synthetic is waiting for you. You can put him down with numerous pulse rifle bursts, but I usually just lob a grenade at him for convenience. Back toward the right will be a second synthetic that requires the same treatment. Watch out--shoot too close to the wall here and you will open up a steam vent right near that switch you need to activate next! In this room are 2 shotshells and a flame thrower canister.
(5) Now open a hidden area in the large central column of this room by lobbing a seismic charge at the column wall on the side opposite the hallway you just came down. Out will pour 4 facehuggers; shotgun them and move inside for the shotgun, flame thrower canister, and shoulder lamp.
(6) This done, move back down the hallway to the area where the 3 derm patch-laden crates were. There is a lift here, but it can be hard to activate if don't stand in just the right spot: face the raised platform and railing, and walk up to it right where there is a small, light green patch just below the black-and-yellow striping on the platform wall. The lift should come down now. Inside is a switch. Activate it and turn left; you will have to dodge a warrior to get to a hypo pack in a now-exposed recess. Be quick now! Dodging right usually works best; once you grab the pack, you will have 30 leisurely seconds in which to pulse rifle both the warriors you released when you hit the switch (there was 1 waiting in a twin recess to the right of the switch, too). Activate the switch in the left recess and grab the flamer canister, then grab the seismic charge in the right recess and walk back onto the lift to go back up.
(7) Walk back to the entrance and stand at the left edge of the stairway on your left, without going down. There is a warrior down there waiting for you. Aim down and to the right and you can get a shot off with the pulse rifle before he is activated. He may run a short distance and then freeze. Pulse-rifle him again and repeat until he is either dead, comes after you, or darts out of sight and you have to go down the stairs after him. Now check the long hall leading out of this large room. There may be 1 or 2 warriors on catwalks on either side of this hallway if you did not activate and destroy them earlier. Aim up with the pulse rifle to grenade them; miss and they jump down to come after you! With all the animate enemies in the immediate area vanquished, go back into the large room. The 2 doors with yellow markings and the words "STAND CLEAR" on them are blowable.
(8) For the one opposite the hallway, select the shotgun and lob a seismic from a distance. With the charge in the air, switch to the pulse rifle so you can grenade the 2 warriors that will be exiting momentarily. If you're lucky, you'll get them both with 1 grenade; usually, it will cost you 2. Inside this room are a med kit, pulse rifle magazine, shotgun shell, and battery.
(9) Behind door number 2 are 3 'huggers, a clip, a seismic charge, a flame thrower canister, and 3 derm patches. Get too close to the window in this room and a synthetic on a platform outside starts shooting at you. If you do it right, you can launch a grenade just above the windowsill and into the synth to permanently send him packing. If you're off even a little, you'll kill him but will meet him again later on at the HARD difficulty setting.
(10) Now go back down the hallway and approach the end carefully. There are a cluster of eggs here and up on the raised platform; there is also a brace of 'huggers lying in wait. There are 3 clips and a derm patch lying out in the open in this area. (If you look down from the platform over the railing where the derm patch is, you can see a barrel and 3 crates below. You can back up and shoot THROUGH the fence here to blow the barrel. For some reason, these crates are harder than normal to blow up when using a weapon, so open them by exploding the barrel). Partially hidden in recesses on the left are 3 eggs and 2 more derm patches.
(11) Now comes the trickiest part of the level. Move forward and down the stairway leading toward the hot grates. Move cautiously ahead to the next stairway. As soon as you see a blip on your motion tracker, get ready to deal with a warrior. Kill him and then, on that same platform, walk toward the fire grates to activate and dispatch a second warrior that will also come after you up the stairs. The shotgun is best here in close quarters because it tends to make the warriors stop momentarily when hit. Now switch to the pulse rifle and run down the stairs and then back up. Grenade the 3 warriors you just activated as they approach the bottom of the stairs (the best place to stand is back a bit from the top of the stairs while aiming down as far as you can). When all is clear, go down the stairs and turn right, moving along the walkway. At the end is a single remaining warrior which is easily grenaded as he tries to dodge on the narrow walkway. Receive only 1 hit (or less) while killing these 6 warriors and you will have done very well indeed!
(12) Now to grab the powerups on the hot grates. The best way to do this is to drop off the walkway and only use the stairs to get back up, since this is a shorter route to the goods and each second you spend down there will cost you 5 armor or health points. Grab the goods on the right-hand grate (nearest all the eggs) first if you have some armor remaining; you will find a pulse rifle magazine, 2 med kits, and a derm patch.
(13) The left grate holds a derm patch, shotshell, and acid vest. If you have the armor (15-20 points or more are needed), drop down away from the vest, grab the shotshell and 'patch, and exit. Now you can go back, drop onto the armor, and make a beeline for the stairs without deviating for the other goods. If you're especially quick, you will get out with 90 armor units; if you're average, it will be 85.
(14) Now continue down the walkway to the fork and go left. Dodge the steam and pulse-rifle the synthetic on the platform ahead. AFTER dispatching him, grab the pulse rifle at the very end of the catwalk. [BUG! If you are using the cheats and have PLAYER INDESTRUCTIBLE on, you can drop off the catwalk here and survive the fall! It is difficult to move around because there seem to be invisible walls everywhere, but there is a battery down here . . . if you can find it! Using the shoulder lamp helps. There may also be an occasional facehugger off in the distance. You can actually reach the battery, but you can't pick it up--not that it would do you any good anyway, since you are stuck down there with no way up.] (15) Now go back to the fork in the walkway and take the right branch. Dodge the fire jets or pay 10 points! Blow the barrel between the crates (if you didn't do it from the egg-infested platform earlier); remember that using the barrel to blow up these particular crates is fastest as they seem to be especially weapon-resistant for reasons unknown. Just ahead will be a synthetic waiting for you unless you made a direct grenade hit on him through that window in the facehugger room earlier in the level. Kill him again if necessary and then move forward to a crate-and-barrel barrier. Blow it and grab the battery and pulse rifle magazine it yields.
(16) Moving past the barrier, you will enter an area resembling a mine. Once inside, drop off the edge on your right to find a secret lift below (it will cost you 5 health points, though, even if you are well-armored). Activate the switch, grab the seismic charge (and 2 med kits, if necessary), and move onto the lift to go back up. Grab the shotshell sitting here, if you didn't already, and continue deeper into the "mine."
(17) Ahead will be 3 warriors and 2 shotshells between you and the exit door. Activate and kill the warriors one at a time, timing your pickup of the shotshells so as not to waste ammo (this only applies if your shotgun is full or nearly so). You can now activate the switch at the end and exit, but you will miss 3 secrets if you do!
(18) Turn and face the wall opposite the switch (at the end of the hall). Blow it to release a warrior. Kill him, enter the room (it holds a pulse rifle magazine and shoulder lamp), and pivot right.
(19) Blow the wall you are now facing to reveal 4 eggs, a seismic charge, and an adrenaline burst.
(20) As you exit these 2 rooms and reenter the hallway, pivot left 45 degrees to face the wall forming the inside curve of the passageway. Use a seismic charge to reveal 4 'huggers, a grenade, and a flame thrower within.
(21) You can now exit the level with all secrets revealed.