Unauthorised walkthrough by Gerty
You start outside in the water and swim forwards to the shore. There will be an SAS man waiting for you. On the side of this lake is a lever; save your game as this is a timed run. Not a very hard one, mind you. Go through door and slide down and end up on a small island (flyby).
Get the flares and dive in the water. Swim into small space (East), stay to the right and open door. Watch out, there are boulders. Get out off the water and kill an SAS man and switch the lever. Swim back and stay on the right side again and up and climb out. Pick up SECRET # 1, some flares and a medipack and swim back out again. Open the door opposite and swim in a corridor. To the right is a medipack and on the left some grenade and revolver ammo and another medipack. Now swim in the middle corridor and get out. Jump over the burners and youíll stand eye to eye with some SAS men.
There is a jump switch and after you pull that, the gate opens and another soldier and his dog will go after Lara. Pick up the goodies that are there. You see a lake and apart from a small medipack, there is nothing there. So go to the left and in that small body of water is the revolver. More SAS men and pick up the Nitron Oxide Canister. On the West wall there is a jump switch and a bit further more ammo. On the floor search for some goodies. You see a ramp on the East side and also another jump switch, that will open a door also on that side.
In the building there will be three SAS men waiting and a dog. Pick up the goodies and the laser sight on top of a box. Enter corridor (North) and run straight through. There are some sentry guns and disable those. On the other side there are two levers and donít forget to pick up the crowbar (cut scene where the Valve Pipe is).
Jump down and you see a room with crates, there is also a door on the left. Open that, you see a lever and some ammo. After using the lever, head into the room. Two SAS soldiers are guarding something there, so kill them and use yet another lever. That is the door where the bike is hidden. I used the bike to drive through that wall and parked it beneath that ramp. Now go where that wall was and go into the corridor and turn left. You see a hole in the floor, youíll be back later, and run further down.
Another soldier and another lever (cut scene of a door opening). Go into that hole and there is a lever that will turn on the lights. Get the Valve Pipe from the box and kill the SAS men there. Go back up and descend that ladder, crawl and jump down. That floor has burning tiles so look where you are jumping. On the last tile there is a crack in the wall and use that. You are now in an icy room. SECRET # 2, the Uzi. On the South wall is a jump lever and something is happening, but what?
Go back into the water and face South, see that hole? Swim through it and a door opens and you are back where you started. Climb the ladder and find the bike. Connect the Valve Pile and Oxide Canister to the bike and go up the ramp. After that corner is a gap you need to clear and after smashing that wall you are outside, so go now to that open gate and jump over the lake. The gate at the end is now open. Get off the bike and after a short crawl to the left, there's yet another lever. Than get back on the bike and drive through that opening on the right, till you canít go any further. Climb the rocks there and after a slide, the level ends.
NOTE: Using the fly cheat in the third run through of this level, I went all the way up in that middle structure where the boxes are and a ramp. Couldnít find a way to jump there and surprise, surprise, two more bikes parked there on the roof and 4 more canisters LOL.