Playing as Lara again and your inventory is how you left it at the end of the Bio-Research Facility level. Kurtis did not manage to turn the power back on, so this is what you need to do now.

First area with gun turrets - Press the button to open the door and exit to the walkway. There are two gun turrets below that are activated if Lara attempts to approach the ladder on the right hand side. To go down, hang from the edge of the walkway on the either left or right (as shown here) and drop down. Crawl to the left and then commando crawl through the small opening in the left wall. Now you can stand. Turn the valve ahead to release steam in the room and prevent the gun turrets from spotting you. Now you can move freely. Wait for the steams to fill the room and climb over the box on your right or commando crawl through the opening again. Do not approach the gun turrets or they will start shooting at you.

Climb up the pipe at the end of the room, behind the second gun turret. Shimmy right and climb up the next pipe. Shimmy to the right around the corner and drop to the metal ledge below. If you do not have enough strength, you can pull on the ledge as soon as you turn around the corner. Follow the hallway and go down the stairs. If you want, press the button at the end and use the security camera to scope what is going on in the next hallway. If you use it, you will see a gun turret at the end of the hallway (there is one more beneath the camera) and a flashlight on the left hand wall.

Second area with gun turrets - Enter the hallway but do not go too far as the two gun turrets will kill you. You can freely proceed until halfway across the third alcove on the left, where the line on the wall is (as shown in this screenshot). You have to shoot the flashlight to explode itself and the turrets. Go in the third alcove on the left hand side and stand just before the line on the wall. Shooting the flashlight diagonally proves to be effective. Turn Lara to face the flashlight an equip your gun. She will automatically aim at the flashlight. If you use the Rigg gun, you will need just five or six shots to explode it.

Go to the end of the hallway, avoiding the right hand part because the steam can harm you. Push the button to open the blue door. Climb up the ladder on the right and follow the hallway to the end. Go up the stairs and the door will open automatically. Go through it to enter the Aquatic Research Area.

Aquatic Research Area - Proceed ahead and the camera will show you a panel which indicates that the power is still down. So, your next step is to restore it by pulling two levers. A mutant fish is swimming around the pool and you can kill it if you want. In the case it is swimming close to the bottom of the pool and you cannot aim at it, jump into the water to lure it and climb out. Be warned though that you will need a lot of ammo in order to kill it.

(Bug note - If you jump into the water and get the mutant fish attack whilst you are climbing up one of the ladders (as shown here), you may activate a funny bug where it follows you outside and starts floating around. It cannot hurt you and you can kill it.)

Restoring the first part of the power - Having the entrance to your back, you will be able to see two doorways with voltage sign above; one on the left and one on the right hand side. Go towards the right hand doorway. There is a part of the pool (in front of the doorway) which is separate from the pool where the mutant fish is. Jump in the water and dive through the broken window. Pull lever #1 on the left to restore the first part of the power and open a door on the other side of the main room (the other doorway with the voltage sign). Continue swimming to the other side and follow the flooded elevator upwards through an opening. When you surface, climb out of the water and enter the next room. Go around the railings on the left and pick up the Small Medipack at the end of the walkway. Press the button on the other side to open the door and follow the hallway to return back to the main area where you jumped into the water.

Restoring the second part of the power - The door you opened before by pulling the lever in the water is exactly ahead, where the other doorway with the voltage sign is. Follow the walkways around to get to that opening and enter the hallway. Pass the door you opened to reach another closed door. Push the nearby button to open it. There is a security camera on the left walkway that shows you the next room. Use the switch on the right walkway to call the elevator. Enter the elevator and press the button on the left to go down. Exit to the room the security camera showed you and go though the blue door ahead. You can see a panel with half of the power on to the left. Pull lever #2 ahead to restore the second part of the power.

Return back to the main area the same way you came: use the switch to call the elevator, push the button in the elevator to go up, exit, enter the hallway and push the button to open the door and get back to the main area.

A brief cut scene shows you a lever, a switch and a ladder.

[Skipping the level\ Note for the PC players - You can take a shortcut here and skip a big part of the level, missing two pick-ups and a kill. What you need to do is to jump into the water and use the lever down there, which leads to the second lever that opens the exit. If you have not killed the fish, it will not be difficult to swim around, as it seems that it does not like Lara's taste. If you are interested in missing the rest of the level, skip to the part of the walkthrough Into the water. It can be done on the PS2 version as well. Very special thanks to Hannah Morrow for verifying it.]

Upper part of the main area - Go up the stairs on the left hand side to reach the top of the room where a movable bucket is. Pull the bucket on the dark blue square on the floor and press the nearby button to move the bucket to the other side of the walkway. Go to the bucket and push it to the room and beneath the metal bars. Pull the lever on the left to throw chum in the bucket. Pull the bucket back to the dark blue square to get a strength upgrade. Press the nearby button to move the bucket back to the first blue square. Push it to the end where initially was.

Go down the stairs and head to the other side of the room where the other opening with the voltage sign is. Go up the stairs and climb up the ladder to the room above. There are two security cameras and each one shows you a lever. The first lever is in the pool where the mutant fish is and the second is in a room you have not been in yet. Exit following the opening opposite the security cameras and follow the walkway to the end. Now that you have got the strength upgrade, you can climb up the pipe. So, climb the pipe, then right, then up again. Shimmy all the way to the left around the sill and drop to the ledge below. Lara has just enough strength to make it, so do not stop at all.

Turn around and press the button to call the metal platform. Step on it to take you to the other side. The door ahead opens automatically as you approach. Press the button ahead to open the door and then press the next button to open the second door. Kill the guard inside. There is a metal locker on each side of the entrance. Search them to find a Mag Vega Clip and a Viper SMG Clip. There is nothing else interesting in this room, so go back pressing the button at the bottom of the stairs to open the door.

Before going back to the main area, go to the room on your right and throw the switch. This will lower the bucket with the chum in the water and the mutant fish will have a new business instead of chasing you.

(Bug note for the PS2 players - It is highly possible the mutant fish to chase you even if you have thrown the chum. You do not have another choice but to kill the fish if you have not already done so, and assuming it is posible on PS2. Otherwise, keep swimming, avoiding the fish, and giving Lara Health Packs if necessary.)

Into the water - Jump into the water and swim to lever #1. If you have followed the walkthrough to the letter, the mutant fish will not bother with you, unless you are a PS2 player and activated the aforementioned bug. If you are a PC player and skipped that part of the level, the mutant fish will chase you around, but this does not prevent you from pulling the lever. By doing this, you open a trapdoor with the number "1" on it and a door at the other side of the pool. Turn around and swim to the other side of the pool passing above the trapdoor. Go through the door you opened and swim upwards to surface.

A cut scene shows Lara climbing out of the water. She changes into a wetsuit and presses a button, raising the water level.

Pull lever #2 to open the second trapdoor. You may want to surface and restore your breath before exiting. Exit through the tunnel and swim through the two trapdoors to end the level.