Building 1[edit]
Go right and then north, ignoring the door for now. On the third screen, open the top door with Pass Card 2 to fill up with truth gas. Then go left. In this screen you will have to be careful not to be seen by the surveillance cameras. Reach the door at the bottom and open it with the Pass Card 2 to find the infrared goggles. Then go back to the second screen and open the door you skipped earlier. Use the elevator to go up to the upper level. Just outside, immediately put on the infrared goggles you found. The machinery around you emits invisible laser beams and if you touch them you will trigger the alarm. With the infrared goggles you can see the lasers and you can move around in order to avoid them. Go north carefully. Here, too, you'll have to avoid lasers. Go left. It seems that you have arrived at the departure of a cable car. When the cabin arrives, go up to the roof. Shortly thereafter, the cabin will leave, and you with it. Be very careful not to fall into the void, or you will die instantly.
You will now have to face a new type of side scrolling area. While on the roof of the cabin, an enemy soldier will look out the windows, in a random order. If you are above the point where the enemy is facing, the alarm will sound and you will be attacked by some flying enemies. As always, only when you have killed them all will the alarm cease and the cable car will start moving again. Fortunately, there is a very simple way to never be attacked. As soon as the side scrolling area begins, immediately move to the rear or front end of the cabin and always remain stationary at that point. The enemy will not be able to see you and you will reach the next stop unscathed.
Building 2[edit]
Get off the cable car and go right. Wear infrared goggles, because here too you'll have to avoid lasers. Go south, enter the door and use the elevator to go downstairs. Kill the enemies and go left, then north. Open the door on the left with Pass Card 1 to find an enemy hostage. Use truth gas to force him to speak. Then go right and then immediately south. Open the door with Pass Card 3 to free a prisoner, but he won't give you any information. Go back and this time reach the door above. Open it with Pass Card 3. Inside you will find Pass Card 6 and the antidote. This is the only opportunity in the game where you can get it, so you should stock it up. At this point, go back to the elevator. Go upstairs, avoid the lasers by wearing the infrared goggles and return to the cable car station. This time you will have to take the one that goes north. When the cabin arrives, go up to the roof like the previous time.
You will now have to deal with another side scrolling area on the roof of the cabin. Follow the same procedure as the previous time, to get to the other side without getting noticed.
Building 3[edit]
Get off the cable car. Go right and then south, avoiding the lasers as usual. Take the elevator and go down to the lower floor. There are a lot of enemies in this room, so be careful. You can't open the door next to you, so ignore it and go left. Open the door on the left with Pass Card 2 to free a prisoner (who will not give you information) and go north. Then go right and open the door at the bottom with Pass Card 4 to find the antenna. Use the door at the bottom of this room to return to the elevator. Take it to go up and reach the cable car station again. Climb to the roof of the cabin that goes north when it arrives. You will have to deal with the usual side scrolling area on the roof of the cabin: follow the same strategy. You will soon arrive at the terminus of the cable car.
Building 4[edit]
Get off the cable car and enter the door. Go right and then south. Jennifer will contact you, to tell you that Nick preceded you and she will ask you to join him. Then open the door on the right with Pass Card 3. Inside you will find an enemy prisoner, force him to talk to the truth gas. Then go north and follow the path until you reach the elevator. Use it to go down one floor.
Go first to the right and open the door you will find with Pass Card 2 to fill up with oxygen tanks. Then go south and open the door at the top with Pass Card 1 to stock up on plastic explosives. Go left and open the door on this screen with Pass Card 4. Inside you will find a prisoner, but to reach him, walk up to the bottom wall of the room! In this room there is in fact a trap in the floor, just like the ones you saw on the train. The prisoner will not give you useful information, but on the other hand, your rank should rise to 5. If you want, you can go back to get the oxygen tanks and plastic explosives in the other rooms, now that you can take more with you. Otherwise, go directly north to return to the first screen. Take the elevator and go down to the lowest floor.
You will now find yourself in a room with three doors. All three lead to a side scrolling area. The first one you should face is the one behind the door to the north.
Side scrolling Area 5[edit]
In this side scrolling area you will not encounter anything that you have not already seen. Proceed by crawling in the first screens, so as not to be identified by the enemies and the surveillance cameras. Then you will meet two pools of water: go under the sensors and immerse yourself. Oxygen tanks shouldn't be missing. Eventually, crawl again to get past the last few enemies.
You will come to a room apparently with no exits, but if you equip the X-ray viewer you will find that there is a weak wall. Take it down with the plastic explosive and go north. In the next screen you can take the boots, the Pass Card 5 and you can fill up on ammunition. Be careful though, because there is a trap in the floor, right in the center. To avoid it, always stay close to the crates. After taking everything, go back and go through the side scrolling area again, backwards, until you return to the room with the three doors. This time take the one on the left.
Side scrolling Area 6[edit]
In this side-scrolling area there are very long pools of water, in which you will have to dive often to avoid the sensors. Sometimes you will have to stay underwater even for a certain time, so if you don't have many oxygen tanks you should go back upstairs first to get some. Then go past the pools of water, avoiding sensors and mines as much as possible. At the bottom you will find some enemies that you should be able to eliminate without problems.
You will come to a room with spikes sticking out of the floor: put on the boots you got to cross it safely and reach the elevator. Go up to the upper level and go left. By opening the door that you will find with the Pass Card 5, you will find the very useful bulletproof vest. Then go north. By opening the door at the top with the Pass Card 4 you will find the bugging kit. Finally, go right and open the door with Pass Card 5 to stock up on truth gas. Heading south will return you to the screen you came from here. Take the elevator, go down and cross the side scrolling area backwards, to return to the room with the three doors. Before taking the last door, the one on the right, however, you should go back to the upper floor and fill up with oxygen tanks, because you will need them in the last side scrolling area.
Side scrolling Area 7[edit]
This is the last side scrolling area to overcome, as well as the longest and most difficult. At the beginning there are some screens in which you will have to crawl to avoid being seen by the enemies. Nothing complicated. Then, however, there is a very long stretch of water. After a first screen with mines and floating sensors, you will have to overcome a very long flooded tunnel, in which, among other things, you will have to knock down seven obstacles with plastic explosives. Better if you have the maximum amount of oxygen tanks that you can take with you, that is 9. You will then have to overcome another pool of water where there are many mines on the bottom, floating sensors and even a surveillance camera. After eliminating one last enemy you will reach the end and enter the final building of the game.