The tram will fly through a gate and crash down in some water. It's up to you if you want to crash with it or jump off in the last second.
The tram has crashed in the water on the other side of the striped wall. Get down there and jump in the water that is in front of you.
Go down the flooded stairs.
Pass the corridor and dodge the leeches. Only your pistol can shoot underwater for now.
You will reach another flooded area. Something lurks in there.
Go left and you will reach a ladder.
From up there you can jump inside the cage and get the crossbow. You can shoot the water beast with your crossbow when you fall down.
Use the valve to open the grate.
Climb the stairs.
Go down there and expect an alien invasion.
Proceed to your right on the pathway. Try not to fall in the water because two beasts are swimming in there.
There will be a rickety looking part of the path. Shoot it before you cross to see where you can actually walk without crashing down.
Make a room for a jump here through the hole in the grate on your right.
Climb up a ladder.
Press the button to start the generator.
The pistons will start moving. You have to time your jumps to cross to the other side.
Kill some aliens in this room then go left.
A scientist will let you inside the big fridge area.
When you step inside the next area you will take frost damage over time so you have to move fast. Many aliens will spawn as well. Stick to the wall on your right and move forward and you will find your way.
You will find a vent that leads down.
Down the corridor you will be attacked by some aliens. When you pass the crates a vort will spawn behind you as well.
Use the lift to go up.
Some guard tries to warn you about something but gets killed by someone.
When you see a big area with many stored containers and crates you have to be on your guard. You will meet the government black-ops assassins here.
The assassins are very fast and agile but if you find a place where their advantage is diminished you can take them out easily. Use your revolver to kill them with one shot.
In the area with crates go to the upper floor to find a surface access lever. Use it to open the nearby gates.
Enter the surface access gates. They will lead you to a single room. When you enter the screen will go dark. Don't worry that is part of the story.
You are caught by the soldiers. They carry you to some place.
The soldiers throw you in the garbage compactor.
You need to jump as quickly as possible up the crates before you are crushed.
You will find a crowbar on the ledge above the compactor.
Destroy the grate to enter the vent that is next to the compactor's crush-plate.