After you beat the boss the first time you'll want to go right as soon as you enter the area.
Over toward the stairs.

Climb the stairs and go right. Once you turn the corner you should come across it.

Go on over and get it.

From after you beat the second boss you'll want to go forward a bit and left at the fork. You should see this area.

Now. You'll want to climb up on top of that container. Take out your pistol and run for the wall behind it. It's easiest to climb if you continue to hold the jump button/key and jump as late as possible. You'll come up to here.

There it is. Right in the back. Go grab it.

Alright. From the enterance of the labs go left. You should see a sorta out of place single building.


Climb on up and grab it.

Right as you enter the labs go right.

See that broken bit there? Go up the ladder to your right and go over to it.

Go over and jump it. (there are other ways to this point, this is just the one I used)
Now follow along until you reach this area.

It's right there. Go grab it.

Mkay. So you've made it to the final boss. Bum rush the back left corner.
Over there.

It's in the toll booth over there.

Right inside it. Nice as simple...if you don't get killed.