Your field computer describes the objective of this level as "Locate a powerful weapon". This is the Super Shotgun, which does two-and-a-half times as much damage as the regular Shotgun, although using two shells per shot. This is a secret level, so the game allows for your not finding and playing it by also providing a Super Shotgun in the Installation.
No particular strategy is needed for this level. Some encounters will come out better if you shoot from cover and at other times you'll need to run and dodge with guns blazing. For the most part, whatever you enjoy most will work fine. As always, be on the lookout for enemies all around, including above and behind you, and keep moving unless you're sure its safe. The path to your goal is easy to find, although completely exploring the level will require you to locate all the secrets, some of which are not all that easy. There is plenty of ammunition around for the Shotguns and the Machine Gun, some Armor but not a huge excess of Health, so don't take damage unnecessarily.
Depending on whether you play this level before or after the Comm Center (before is best, to get the Super Shotgun), you may be meeting Flyers and Parasites for the first time. This early in the game, successive levels increase noticeably in difficulty, so consider leaving the Armor, Adrenaline and Stimpacks to be picked up just before you leave so that you enter the next level in good shape for a tough fight.
Tip: If you already have a particular type of weapon or other item, attempt to pick up any others that you find. You can carry multiples of most items. Each weapon you pick up adds to your ammo supply for that weapon type.
From the elevator, take a left and follow the only available route. As you will be coming back this way, consider leaving the health and ammunition that is scattered around to be picked up later, when you may need it more. You will meet two Light Guards, turn to the right and then arrive at a square door. If you approach the hatchway that you passed on the left, you will receive the message "ACCESS DENIED Door is opened elsewhere". Through the door that does open is what looks like a subway platform with some packing crates and exploding barrels on it. Periodically, one of two tram cars stops briefly at the platform and then continues. There are two Enforcers here, around a corner to the right. Keep clear of the barrels as you fight them. See Secrets, below, either now or when you return here later on.
Before you leave the platform, take a note of the area below, in particular the steps coming up from the left and the large doors that open to let the tram through. Get into either tram car and ride it down to the lower station, where there will be two more Enforcers to welcome you. Equip the machine gun during the ride and leave the tram car already firing. Keep moving to avoid the return fire from the Enforcers and also from a Shotgun Guard in an opening up above you. As soon as you can, get through the door that leaves the platform on the right. This will take you around a U-turn to a combination of stairs and a long ramp. Run to the top of the ramp (but no further) and then run back down backwards.
Shoot the incompetent Guards and take the Key.
Some Light Guards will come around the corner at the top. Make them come to you and use any weapon to kill them.
Now run backwards to the top of the ramp and you will see a landing that was above your head. If there is a Guard up there, shoot him. Keep a watch at your back in case one of the Light Guards did not come out before; there will be three at hard difficulty. Shoot the glowing, pulsing button on the landing edge and the ramp will rise up. Equip the Shotgun and walk over the raised ramp to the landing. Turn the corner to the right carefully because there are four Shotgun Guards there (three if you already killed one). You will see that they were guarding the Red Key. Take it, you'll need it quite soon.
Go back to the long ramp, which has probably lowered, so just drop down (also see Secrets, below, now or on your way back through here). At the top continue up the steps and around to the left, watching out for any Guards that did not come out before. If you look through the opening on the inside of the turn, you will see across to another opening from which the Guard near the Red Key may have attacked you when you arrived on the platform below. If you'd come up here earlier, all four Shotgun Guards would have been able to shoot at you, but now they're dead. Left again and you're facing another square door. Beyond this and a second door are Enforcers (four at hard difficulty) and Shotgun Guards (also four). Two of the Enforcers will be on a ledge to the right and above you just as you go through the first door. Either the Shotgun or the Machine Gun will work, but note that Enforcers often drop Machine Gun ammunition when killed. (If you're low on health at this point, see Secrets, below, otherwise leave this one until later). The path ahead takes you along a hallway to a door.
On the other side of the door, you will quickly encounter an Enforcer and a Light Guard. You will be facing a rock wall, but there are openings into a large cavern both to your right and to your left. Keep a watch for enemies on both sides and use the rock wall for cover as you pick them off in the cavern. There are more Light Guards and two more Enforcers on a round metal tower in the middle of the cavern. There are also two Flyers. Notice the whooshing sound that they make which will let you know how near they are and will stop when you kill the last one.
Kill the Enforcer and the Super Shotgun's yours.
When you consider it safe enough, make your way down the left hand side into the cavern and around the tower to the elevator platform. This will take you up when you step on it. Go across the top of the tower to the computer. If you approach the computer without having the key you will receive the message "You need the Red Key". Go back and find it. Otherwise, the bridge will lower. Equip the Machine Gun and go across the bridge to the door on the other side. After a brief fight, you will have the Super Shotgun and plenty of ammunition for it. Yay!
Now that you've got what you came for, begin to retrace your steps to the elevator back to the Comm Center. When you open the door to leave the Super Shotgun room, some Flyers will have appeared from nowhere. They will probably be right outside, somewhat below and on either side of the door. One blast each with your new toy will do it, or run, drop down and keep running if you're not interested in getting all the kills. (See Secrets, below, before you decide to leave this area.) On your way back to the long ramp, you will meet more resistance that wasn't there before. If you don't want to pause for the kills, just run and dodge and you won't take too much damage. (Keep an eye out for another Secret, if you didn't search it out on the way in due to low Health.) When you reach the platform, however, you may have to wait for the tram car, so consider taking out the Flyers from the opening above, where earlier you looked across to the Red Key area.
The tram car will take you back to the upper platform. As you approach, recall the large doors that open to let the tram through. As soon as you're through these, get off on the wrong side. When the tram moves away, swim across the water, get out and look back. A welcoming party will be gathering on the platform, especially on the right. Use the Blaster to shoot the exploding barrel there. Swim back over the water and shoot the other barrels if they are still there. Climb the steps to the platform and make your way past the remaining resistance to the elevator, collecting items and ammunition on the way. If you're not interested in scoring all the secrets and enemy kills, push the button and the elevator will take you back to the Comm Center.
If you run past the newly appeared Strogg on the way out, you can complete this level with as few as 34 out of the total of 63 enemies killed. Even if you fought them all, you may still be short of kills. To score these, you'll need to find all the secrets (see below) because four enemies are in secret areas or won't appear until you pass through a secret area. Others you will meet on the exploration that leads to one of the secret areas. You may still be one short, in which case search the area off to the side of the upper platform where earlier you found two Enforcers.
In the area to the side of the upper station platform, where you encountered two Enforcers on arrival, there are two stacks of crates. Behind the small gray boxes on the larger stack is a Silencer. If you jump and create some light by shooting your Blaster, you can just see it. Climb the smaller stack and run / jump across to the red box on the top of the larger stack. Again use your Blaster for light to see the Silencer and drop down. You will receive the message "You have found a secret". If you have a silencer already, you may not collect this one, but you will still score the secret. Jump over the small gray box to get out.
The round metal tower from which you lowered the bridge to the Super Shotgun room is surrounded at the base by water. Enter the water on the side opposite to where you came into the cavern. Dive down and you will see a recessed panel in the foundation. Shoot it to made it rise up. Beyond are two Barracuda Sharks. This is your first meeting with this Strogg type. They can't hurt you from a distance, but close up they can take a bite out of your health. Use either the Machine Gun or the Shotgun (or the Super Shotgun, if you have it). Come up for air after the fight and dive again to go through the opening. Surface inside the tower and receive the message "You have found a secret area". Here you will find an Invulnerability, Jacket Armor and two MedKits. Drop into the water and swim back out to continue.
On the way from the Red Key to the Super Shotgun, you pass through two closely-spaced doors while fighting Enforcers and Shotgun Guards. Two Enforcers are stationed on a ledge between the doors. You can get to the ledge from the area on the other side of the second door. At the back of the ledge you will find a small concealed area with a glowing button and a gun trap below. Shooting the button (use the Blaster to conserve ammunition) does two things. First, it opens up a panel to the left of the gun trap. Second, it sets off the gun trap. As soon as the gun trap stops, drop down, go to the left where the panel rose up, dropping again and moving to the left to get off the platform that begins to rise under your feet. If you don't make it off the platform, back away from the edge until it goes down again but not so far that you set off the gun trap. Once you're off the platform in the water below, explore and you will quickly find a short pipe with rubble and an Adrenaline inside. Enter to take it and receive the message "You have found a secret area". Go back to the platform and let it take you up. The gun trap is permanently disabled, so you can safely continue. You can also get to this area from between the doors, just be more careful about the gun trap because you are on the same level.
Stand near the bottom of the long ramp that you used to reach the Red Key. With the Blaster, shoot up at the glowing button to raise the ramp but run quickly off the lower end so that the ramp goes up without you. Go under the ramp, using your blaster for light. You will find a MedKit, which is no big deal, but you will also receive the message "You have found a secret area". If the ramp drops, use the wall button to raise it again to get out.
Sign on wall opposite lower station platform.
There are two ways to get to this secret. The one described here is not the usual one, but results in the most complete exploration of the level and the most items collected. From the platform of the lower station, where there is a sign on the wall opposite, drop down to the solid ground to the right and go to the side away from the platform where you can stand clear of the tram car and look down. There is water far below. If you can see any Barracuda Sharks swimming about, it's a good idea to kill, or at least hurt, them from here before you dive in among them. A Grenade is useful, especially if they all cluster together. Keep an eye on the grilled opening to your left and if a Parasite appears there take it down using the recess you are standing in for cover. When you are ready, equip the Super Shotgun and drop straight down into the water. Kill any Barracuda Sharks that remain. You will see an elevator platform in an alcove nearby. Before you take it, explore the watery area all the way to the other end, where you will find useful items, including Grenades. At the top of the elevator you will immediately face a Guard; one Shotgun blast and he's down. Step out of the elevator and turn to the right. If you did not take out the Parasite already, it's right there in your face so have the Super Shotgun ready. Advance into this area and receive the message "You have found a secret area". Keep going and shoot the Enforcer who is expecting you to come from the other direction. Go down the ramp into water again, turn right and find another elevator platform. This will take you to a hidden area where you can collect more items. Approach the angled recess in the wall and a panel will drop to let you out over the station platform. To avoid fall damage, crouch and drop onto the crate below.
To complete the enemy kills you can try the usual approach to this secret now. Drop off the platform in the middle. Dive, look to your left through a tunnel and shoot the glowing button that you will see at some distance. There is also a Barracuda Shark over there. Turn quickly to your right and you will see a panel open. Another Barracuda Shark will be in there. Go in and you should recognize where you are from the first exploration. Either swim back out or take the elevator again to return to the platform.
From the platform of the upper station (where you arrived) drop into the water, dive down and swim to the left through the tunnel that you will easily see there. The tunnel turns to the left and ends at some steps. Go up the steps and out of the water to receive the message "You have found a secret area". A corridor lies ahead along which you will find Armor Shards, StimPacks and a Rebreather.The rubber duckie easter egg. If you already have a Rebreather, you may not be able to pick up this one. After a left turn, the corridor ends at the other side of the hatchway that you passed very soon after arrival in the level. Press the wall button on the left to open it. As you step into the hatchway, a Parasite drops down from above. If you can get two close-range hits with the Super Shotgun, it's dead. Through the hatchway you should recognize where you are. If you went for this secret on your way out of the level before clearing away the newly appeared Strogg, you will need to fight them now.
After you have killed all the enemies that are likely to be able to get to you on the tram car, step onto it and go make a cup of tea or something. When you have ridden around the loop thirteen times, an easter egg will appear. Superimposed on the sign on the wall opposite the lower station platform is a picture of a rubber duckie with a bloody bullet hole in its head.
