Test Facility
As you get off the elevator, follow the red carpet forward. Turn right when the hallway splits and go into the room on the left side. You'll find a keycard on the desk inside. Take that back into the hallway and go left this time. Use the key card to open the door into the next area. Make your way through the next room and find the fire alarm on the right wall. Just to the left of that will be a column and a long counter. Hit the alarm and then take cover behind the counter.
Wait for the guard to come and investigate the alarm, when he walks past you, sneak into the room that he just left. The guard in the room won't notice you so just walk to the left and pick up the notes off the table. With the notes, you can leave and head back to the room where you found the card key. In this room, you'll find a computer across from where the card key was. Use this to open the wall in hallway.
Go through the newly opened door. Follow the hallway to an elevator and ride that down. Watch the cinematic to learn a very important lesson. There are mines everywhere. That's ok because you're just going to go around then. At the bottom, go directly to the left and you'll find a large ladder leading to the catwalks above.
Watch out for guards as you move along the left side of the cat walks. When you get to the last bridge leading right, wait for the guards to finish their conversation and when they disperse, follow them across the bridge to the right side. When you get to the right side, turn left and then head into the small entrance on the right side.
You'll be on the second floor of the lab structure. Go down the stairs to the left and at the bottom will be a couple of security guards that are talking about the upcoming fight. Wait for their conversation to finish and deactivate the security system by using the computer on the desk. Now, go into the next room where a scientist is looking at a drawing board. Go through the door that leads out of the room.
In the cave area that you enter, turn left and walk past the first left. At the second left, turn again and use the checkpoint. The checkpoint is a safe spot so feel free to wait here. If you wait patiently, the doctor will come near here and you can strangle him. Do that and you've also got a crate nearby that you can use to dump the body.
When the body has been dumped, head back up to the catwalk the way you came down from it. Make your way back to the ladder and go down to the bottom. At the bottom, hug the right wall and follow it past the elevator you came down on. Beyond that will be a long hallway with double doors at the end. Go through the doors.
Decontamination
Inside the next hallway, hug the right wall. You'll see some benches on the right and one of them will have a bottle. Grab the bottle and then take cover against the wall. Move along the wall and then swap to the next section of wall to get past the door. Go to the end of the hall to find a locker room. As soon as you enter the locker room, turn left and go through the open door way.
This is the decontamination shower. Continue straight ahead and watch for the valve on one of the walls to the right. Activate the valve and then go around the back of the showers. Go to the far side and head back to the entrance of the showers so that you are approaching the door from the right (it will be on your left).
Go through the door back into the locker room and hug the left wall. You'll see another doorway ahead with plastic cover it. Peek your head through the doorway and then throw your bottle over the guard's head at the stairs beyond. He will go to investigate and when he does, make your way to the vent on the right wall. Climb through the vent and come out on the other side.
You'll find yourself in a small bathroom next to a lounge where a group of guards are watching TV. Your main concern is going to be a researcher who will walk into the bathroom to use his locker. Make sure that you are on the lookout for him. If you don't see him coming, round the corner into the lounge quietly and use the computer right next to the door. On coffee table in front of the guards will be your Evidence but it requires a disguise. When you are done with it, head back to the vent and start crawling through. Make sure that the guard has returned to his chair before coming out and going to the red doors he's guarding.
R&D
Unfortunately, I'm not sure that there's a way through here without using a disguise just because the guards are too dense. For now, slowly move down the stairs to the left. There will be a guard below on a piece of catwalk that goes out over the center. Watch him because he may leave that post and come up the stairs towards you. If you can get past him, aim for the double doors just behind him. Go through the doors and immediately go down the stairs just to your right.
You'll enter a small shop area. There are several pieces of cover in the middle of the room and Fire Paste in the corner. Run around in one part of the room but then quietly take cover to lure the nearby guard into the room. When he comes in, subdue him and take his outfit. Grab the fire paste and go up the stairs into the previous room. In here, you'll find two scientists working quietly who will take no notice of you. There will be a beaker with a green liquid inside. Place the Fire Paste in there and eventually, Dr. Valentine will kill himself with it. As soon as you are done, go back down the stairs and through the doors onto the catwalk.
Walk down the stairs of the catwalk to the left and you'll see a guard at the corner. It IS possible to get past him by using a diversion but not a disguise. It requires you to go into the room to the left, however, which is a very busy room. Instead, just use your instinct to blend and walk into the side room. Go down the stairs here to get another floor lower.
In this room, you can pick up Dr. Ashford's recording and hit the checkpoint. Grab the notebook on the counter by the door and then walk out of the room. Continue down the catwalk and get to the bottom floor of the facility. Go around the central area and to the far side from the stairs. You'll see a couple of large red pipes coming up out of the center that meet in the middle at a valve. Open the valve and then make your way over to your target. Kill him however you like and then walk back across the facility towards your exit.
It is possible to kill him with a quiet melee attack of some kind even if he's right next to somebody. The smoke screen is pretty fantastic. Make use of it however you like. During this time, you can also get the Evidence on a table next to a couple of privacy screens. When you've gotten close to the exit, trigger the bridge and then take cover behind the console. This will keep you from having to expend instinct to stay unnoticed.
Cross the bridge and enter the lab room. Inside, there are two electrical boxes to sabotage. Destroy them both and watch the video records near the bed if you like. When you are done, leave through the double doors.
