Portal/Escape 2

You've leapt down to the next area and advance forward, only to have the floor opened beneath you.

Turret ambush


The pistons separate, causing you to fall down into an area with limited cover. The door on the right will open first, revealing a turret, followed by the middle door, and the left door. Behind each door is a turret.

You will have to take out each turret quickly — knock it over or throw it through a portal.

The third door will have an exit. Shoot through the opening and proceed to the next room containing a glass pipe. Shoot a portal above the pipe to walk on it, and jump from the pipe to the catwalk.

Fling


After disabling the turret, a door should open in front where there is a broken catwalk. Walk forward to the "over here" text, turn around and shoot a portal on the opened door. Enter a ground portal, and fling yourself to the catwalk.

Rocket turret
You are back in the observation area, with a forcefield to your left. Walk through it and press the button — this deploys a rocket turret which will seek you and fire a rocket, shattering the glass window.

Walk behind the turret to the next glass window. The turret will fire a rocket, but will hit the window as you dodge. Go through the corridor to reach yet another glass window; here you will need to place a portal on the opposite wall, and a portal within the turret's room. Trick the turret into firing a rocket at the wall.

In the next room, you should see a glass tube for moving storage crates. Redirect a final rocket to this tube and grab a storage cube that falls out. Place the cube in front of the vent and climb into it. Alternatively, a chair from the previous room works.

At the end of the vent is a fan; while you can't climb down, you can shoot a portal to bring you into a small sewage area. Shoot a portal above the metal platform and walk across it.

Note: Although you can redirect a rocket to itself, it is immune to its own attacks.