(1) This is one of the hardest levels to complete safely. There are numerous areas with a large potential for causing serious damage, and several additional locations where the probability of being facehugged is quite high. At the very start of the level you can kill the first enemy without even leaving the entrance chamber: turn left slightly and grenade the frozen alien handler standing in the distance. For some reason, this individual enemy occasionally survives a direct grenade hit. While the alien handlers are without question the deadliest of the human enemies, they are not really much of a threat. On this level, however, it will be easiest to simply grenade most of them to prevent their constant annoying return. As you move out, you will see a second alien handler across the acid canal and to the right; grenade this one also.
(2) Now stay left and round a corner, ready to deal with another handler waiting here. Dispatch him (he coughs up a pulse rifle magazine) and open the first secret area by lobbing a seismic charge at the wall to your left just past this corner. If you are quick you can switch to the pulse rifle while the charge is still in the air and be ready to deal with the 2 facehuggers that immediately emerge. As soon as you can safely enter this new hallway, 2 adult dog aliens emerge from a recess in the right side of the wall. Pulse rifle them and enter the recess they were hiding in for a flame thrower. Now throw another seismic charge at the end of this short hallway to reveal a hidden room containing a switch and acid boots. Activate the switch but leave the boots for the moment. Now turn and move forward slightly to activate 2 new adult dogs that just materialized in the flame thrower recess--you know what to do.
(3) Now switch to the smartgun and prepare to move quickly. The best strategy is to BACK into the acid boots you just found and then dart forward out of the secret area. Stay along the wall on your left until an acid canal blocks your forward progress. Pause here for a second (you are trying to get as many facehuggers as possible within the acid canal to follow you) and run to your right until you reach a ramp heading left down into this canal. The following 'huggers should be ganging up at the bottom of the ramp. Aim down with the smartgun and eliminate these facehuggers with 1 to 2 bursts. (Keep your eyes open for a lone facehugger that may attack from the unexplored walkway ahead and to your right at about this time.) Now switch to the pulse rifle and wade on in. Run to the end of this canal for body armor and 2 med kits, watching for any 'huggers that may not have followed you to the ramp (there are 5 'huggers in all). (Be careful in the canals as any facehuggers down there are hard to see due to the turbidity of the acid, forcing you to rely heavily on your motion tracker.) Do an about face and go up the ramp to exit the acid. The ramps are slippery and getting up them without overshooting (and landing in another acid canal) when you reach the top can be tricky. The surest tactic seems to be to hold the RUN button down continually until you are very near the top of the ramp, and then switch to TAPPING the RUN button. The second you are off the ramp, stop yourself short with a REVERSE tap on the controller. If you are quick, your acid boots won't run out until after you are on the ramp and out of the acid. Another alien handler will be on the scene by now, firing at you while you are trying to concentrate on making it up the ramp safely. Turn to your left and grenade him and continue ahead.
(4) You will reach a T-crossing shortly; go right. Activate the switch you dead-end at and look right to see a lift moving up into place to fill a gap in the walkway across the canal from you. Now wait here a few more seconds for another alien handler to come walking toward you on the walkway to the left of the lift you just activated; grenade him. Go back to the T-junction.
(5) If you are absolutely desperate for shotshells, there are 3 in the acid canal below. Face the T-crossing the way you originally approached it. Drop off the walkway into the right corner formed by the top of the T: there is 1 shotshell here as well as the acid boots that will keep you from getting scalded while you grab the other 2 shotshells and make your exit. Stay right (to the bottom of the T) for another shotshell and then do an about-face. Stay left past the T-crossing until you are to the right of the switch you just activated for another shotshell. Quickly eliminate the alien handler wading around in this area. Now to get out: do a second about-face and stay left--straight ahead and around the corner brings you to a ramp. If you went for the shotshells (I recommend against it due to the potential for serious acid damage and the presence of multiple facehuggers), you will run through this next part of the level in reverse; there is one area where a lift will still be down but you CAN cross where the 2 corners of the walkway meet.
(6) Assuming you let the shotshells lie, return to the T-crossing and go straight ahead (this would have been to the left when you originally arrived at the junction). Stay to your right until you encounter an alien handler below you in the acid canal to your right (you will have a wall to your left again). [BUG! Part of the walkway here drops down later on in the game to allow you access to the second half of this level. If you stand near the wall by this lift, an adult dog on the other side of the wall may hit you THROUGH the wall and actually cause damage. This is particularly unusual because the adult dog is actually 1 story below you when you enter this part of the level.] Switch to the shotgun so that you can more accurately aim a seismic charge down at the alien handler when he approaches; the easiest location to fire from is the portion of the walkway that allows you to look straight down the section of canal the handler is wandering, although you may have to wait for the enemy to come within range of the charge. This done, you will want to deal with some facehuggers running around in this same area: standing with your back near the edge of the walkway behind you, aim down with the pulse rifle (or smartgun, if you think you can spare the ammunition) and shoot into the acid at the 'huggers moving back and forth within the canal. You may have to position yourself to face the other "leg" of this L-shaped portion of the canal (and even dash from one end to the other to put some distance between you and the facehuggers), to eliminate both 'huggers here.
(7) This done, you can continue ahead along the unexplored portion of the walkway. Stay right to a third switch (you will kill an alien handler off to your left en route) and activate it; rotate left to see a facehugger running off the lift you just raised and come for you across the walkway. Kill it. Two more facehuggers will have arrived by now down in the acid where the wading alien handler was. Repeat the sniping tactics you used to kill the previous pair of 'huggers in this same area.
(8) Now move forward to the unexplored portion of the walkway ahead. Just past the lift you just activated, you will arrive at another ramp leading down into the acid. There are 2 perilous secret areas to be explored here, but before taking a dip, grenade all of the 5 alien handlers here (each standing in his own small alcove against the wall). Several will cough up a pulse rifle magazine upon expiring, but only 2 magazines--from the first and fifth handlers--usually fall within grabbing range. The other magazines almost always fall uselessly on the platforms next to the expiring alien handlers. And NO, there is no way to get up there! (Take special note of the locations of the first 2 handler-containing alcoves. Also take note of the small, rectangular acid pool in front of the fifth alien handler, as you will be entering it shortly.) Beware, as 1 or 2 'huggers may attack you on the walkway (often from behind) while you are accomplishing this.
(9) Foes vanquished, return to the ramp. Select the flame thrower, run down into the acid, and immediately dart into the recess on your right which contains desperately-needed acid boots. Now rotate to face the wall directly under the alcove the first of the 5 alien handlers was in. Run up to the wall and a lift lowers to reveal a secret room. Four facehuggers are inside, and you will need to dart partway into the room to lure them out. You may end up raising and lowering this lift several times (by dashing in and out of this room) before all 4 'huggers emerge. Be careful as the probability of being 'hugged is quite high here. A pair of night vision goggles--pretty useless on this particular level--are on the lift, as well as the expired alien handler's pulse rifle magazine (if it landed just right). Enter the room itself and grab the hypo pack on the left. You now have an additional 30 seconds of protection to explore the next secret. If the lift rises (blocking your exit) while you are in this room, move back to where the hypo pack was to reactivate it.
(10) Run back out into the acid canal and lower another lift located under the second alien handler alcove in exactly the same manner. This secret room also holds 4 'huggers; draw them out to kill them (exactly as you did at the previous secret room) or take your chances by moving directly inside and turning right to meet the threat. Often, the fourth facehugger stays put and tries to ambush you when you enter. Beware, as this is another place where the probability of getting hugged is quite high. Having killed the aliens, grab the pulse rifle and (if needed) the med kit. If this lift rises, trapping you inside the secret room before you can exit, just move back to where the pulse rifle was to reactivate it.
(11) Now make a hasty retreat out into the canal and back up the ramp. Watch out for stray 'huggers wandering the canal in addition to the 8 you will kill in these 2 small rooms. If you were quick, the combined acid boots and hypo pack have protected you long enough to exit safely. Low on armor by now? You're in luck. After getting up the slippery ramp, move straight forward and drop into the small acid pool directly ahead. Stay RIGHT as you drop into this area (an acid vest is on the left, and if you already have some armor left you will want to grab the vest on your way OUT of the acid rather than on your way in). Stay forward and turn 180 degrees. You will see the vest, as well as a lift here (the same one you raised by activating that third switch) which just dropped down to let you back up. Run onto the lift (nabbing the vest on the way) and it will raise you back up to the walkway and out of the acid.
(12) Now move to the even smaller acid pool in front of that fifth alien handler alcove that you noted earlier (this was the only other alien handler whose pulse rifle magazine may have landed close enough for you to grab it). Below are a grenade and a very determined facehugger, but you have one quick chore to complete first. Go ahead just a little farther to another ramp. Aim down and wait a moment for any nearby 'huggers to come up it after you. You may have to run partway down the ramp (stay out of the acid!) to draw any nearby facehuggers to you. These distractions eliminated (there will usually be between 1 and 3 'huggers), return to the small acid pool. Turn so that the fifth alien handler's alcove is directly behind you. Choose the flame thrower and BACK off the edge into the acid without slowing while in RUN mode. You will pick up the grenade and see the facehugger in front of you and coming fast. Kill it and run onto the section of walkway that dropped down as soon as you stepped off it. Don't overshoot or it will rise behind you and trap you outside this small area and in one of the main canals. The other mistake to avoid is not being quick enough and having the lift rise before you can get onto it. If this happens, back up again to lower the lift and then run onto it without slowing down or stopping until you are directly on it.
(13) Once you are back safely on the walkway, prepare to enter the second half of this level. DO NOT go down the stairs past that last ramp or you will be stuck at the exit area with no way to explore the rest of the level. This gives you only 23% for SECRETS and you may restart at the beginning of this level when you go into the exit chamber. Instead, backtrack to the rectangular acid pool where you found the acid vest. Stopping just short of the lift that allowed you back up out of this pool, turn left to look into a small cul-de-sac of the acid canal. You should see a switch in the acid at the FAR end of the cul-de-sac. Opposite the switch (and directly below and in front of where you should be standing) is a pair of boots in the acid. You want to drop directly onto the boots to avoid any acid damage and run straight to this switch. Prepare to run like crazy. Activate the switch, turn so that the switch is immediately to your right, and stay to your right around this L-shaped portion of walkway. At the top of the L where the canal ends a lift to your left will be down (this is also where you encountered that alien handler wading in the acid), and you need to go through as rapidly as possible. This is the fastest dash in the entire game! On your way there, an adult dog alien may emerge from this new area and have to be eliminated before you can enter: use a grenade and avoid slowing down if at all possible. Facehuggers roving the canal can also slow or stop you, and if any are revived in the immediate area, you may wish to eliminate them with the pulse rifle or smart gun before dropping off the walkway into the acid. If you are too slow and miss the lift, you will have to backtrack to the switch, activate it, and make another mad dash for the opening.
(14) Once inside, slow down quick! You want to activate the 2 adult dog aliens directly ahead 1 at a time. The closest is to your left and will remain frozen if you approach cautiously; the second is directly in front of you across an acid pool. Occasionally, the adult dog that would otherwise have greeted you just outside in the acid canal may be waiting for you here instead. There is a pulse rifle magazine in the far right corner. As you move around, be careful to avoid the bluish acid puddles on the floor as they will cause damage. There are a lot of them, but by navigating carefully you can avoid nearly all of them. You will want to use a grenade (or seismic charge) on ALL enemies within the next portion of this level to prevent them from reviving later in the game. The reason is that you will be returning to all the acid pools within this part of the level to grab the powerups within them; there is only a single pair of acid boots in this area, and time will be of the essence once you don them. Even a single revived adult dog can slow you down enough to force you to navigate 1 or 2 acid pools after your boots run out.
(15) There are 2 corridors exiting this room; take the right one. There will be 1 adult dog within the corridor itself and another inside the next room. This is an ideal area to use seismic charges in order to conserve your grenades. Switch to the shotgun for accurate aiming, and attempt to lure the dogs after you into the narrow corridors where you can launch a charge with a high probability of scoring a direct hit.
(16) Use the same technique to eliminate 3 dogs in the next room. This room, which is a bit larger than the last one, has 2 corridors entering and exiting it.
(17) You now want to backtrack by taking the corridor adjacent to the one you entered the room by. In the room ahead is a shotshell and, if you were NOT greeted by an adult dog just before (or after) finishing your mad dash to enter this part of the level, it is waiting here. Incidentally, if you continue back toward where you entered this area the corridor leading out of this room has a completely unavoidable acid puddle within it (another reason to enter this room from the direction you just did).
(18) Now head back to the larger room you just came from. Kill a single adult dog in the room at the end of the left unexplored corridor and then back up and go into the right corridor. On the way you will pass a shotshell and acid boots--leave the boots for later. In the room ahead is another shotshell and 2 adult dog aliens. You will need to react quickly to kill these aliens with seismic charges as this corridor is very short and leaves you less time to aim.
(19) Now move toward the single, wide corridor exiting this room. There are 2 adult dogs ahead, and killing them with seismic charges will be especially difficult because the wider corridor gives them more room to dodge.
(20) This feat accomplished, go back to the acid boots. You will need to explore all 6 acid pools in this area in order to score 100% for SECRETS. The acid boots barely last long enough. Back into them and then dash through the acid pool in this room for a grenade and pistol clip. Take the right corridor (of the pair to your left, leading back to where you entered this area) and stay left to 3 previously-explored rooms, each with an acid pool. Of these, the first pool holds a shotshell and clip, the next nothing, and the third a clip and grenade. You now end up in the room where you grabbed the acid boots. Move quickly forward to the right corridor to grab the grenade and med kit in the next pool, then backtrack into the acid boot room and take the left corridor to find a pair of clips in the final pool. Your boots very likely ran out before that last, painful dip!
(21) There is one more area to explore here before moving to the exit area of this level. Backtrack yet again to the acid boot room and take the right corridor that led you to that second-to-last acid pool. Go through the wide corridor to an unexplored area. Directly ahead is a switch. Activate it, turn around, and move to the wall on your left. When you stand in the right spot (directly in front of the closest of the 2 gray "beams" in the wall), the floor drops to reveal a small secret area at the far end of the lift. Within are 2 adult dogs and a 200-point adrenaline burst (if you've been doing well, you won't need it). You can pulse rifle these dogs as you will have a relatively easy opportunity to grenade them shortly.
(22) Now activate the switch in the secret room and stand in the same spot on the lift as you did to lower it; this time it will go back up.
(23) Now exit this room by entering a very long corridor at its far end. There will be 3 adult dog aliens of the ceiling-hanger variety in this area. Use the smartgun (you'll find more ammunition for it shortly) to dispatch them. [For a neat trick, kill all 3 in the room at the end of this hallway--see below.] Because this is the highest you will have to aim to hit any enemy, you will need to keep your distance to be able to kill them. Move all the way to the end of the corridor; you will encounter the only absolutely unavoidable acid puddle in the entire game about halfway down. At the far end is an acid vest which you will very likely need by now (in spite of the body armor you found near the beginning of this level!). Do not drop off the ledge here into the exit area! Instead, wait until 2 or 3 adult dogs are drawn to you and kill them with the pulse rifle (you can try seismic charges, but they move too quickly for consistent success). Drawing the aliens to this location will make your entrance to this area (from a different direction) significantly easier later.
(24) Now backtrack. You will take another hit crossing that acid puddle. When you near the mouth of this corridor, switch to the shotgun (for aiming seismic charges) and revive the 2 dogs you pulse-rifled here earlier 1 at a time. Each presents an easy target when it follows you into the long, narrow corridor. Now stay right to end up by the very last acid pool you explored during your 30-second marathon with the acid boots. Drop off the ledge here to enter the last area of this level. Two adult dogs will immediately attack; smartgun them in their tracks if you feel you have sufficient ammo, since a smartgun magazine is dead ahead (keep the ammo rounding trick in mind). Cautiously move forward; another adult dog alien or 2 will attack from the left side of a very large acid pool in the room you are entering. Pulse rifle or smartgun them and approach the corridor that leads out of this large room. Beyond it are the 2 or 3 adult dogs you led out of this area earlier; they will be much easier to deal with now. Kill them as they re-enter this room. Before moving on, run across the middle of this large acid pool for the smartgun magazine (notice that the pool is narrower in one direction than the other--no sense wading any longer than necessary!). There are also 2 med kits in opposite-facing corners of this room.
(25) Now proceed into the very last part of the level. Beware as there are 3 facehuggers in the walls here that all seem to be extraordinarily good at 'hugging! As you turn left and move up the corridor, 1 is on your right and 1--perhaps the most dangerous--is on your left just past the exit chamber. There is a third 'hugger at the very end of the corridor here, too. (Look up these steps and you can see the area you were advised NOT to enter earlier at the risk of having to replay the level.) [PSYCHEDELIC ALIEN HANDLER TRICK: The 3 ceiling-hangers you led to the acid vest area and killed earlier will be revived at the opposite end of this corridor as orange splotches on the floor. Shoot them (and even walk on them!) until all are re-killed. Up from each will pop a red/orange/blue alien handler! The 3 handlers make quite a spectacle, especially if they all walk in the same direction and stay relatively close to each other. I even once had one enter the exit chamber with me, although he didn't follow me into the next level!]
(26) Now you are ready to make your exit. If your health and ammunition levels are close to what they were when you entered, you have done quite well.