Portal/Escape 3

This is the last part of Portal. Once you complete this, you may get the heartbreaker achievement.

Getting to the top
Get past the sewers and at the end you see a wall that's portal-friendly. Get there. Now just try to portal out of the gooey – but not lethal – water. Once you get to the surface, you hear an alarm and turrets will shoot you to death.

Try to take cover as they shoot you and while they shoot, put a portal behind them and put another near you (wall or floor, your choice). Then take them out.

Once you take out all of the turrets, find the turret that's on the highest floor. Put a portal in that alcove, and put a portal nearby. Once in that location, scan the room for a slanted wall. Once you find it, put a portal on top of it.

Here's the trick to find a few more turrets: Put another portal near you, then pass it. You may fall and put another portal in time before you land. You are flinging in the sky. Your super jump is not high and fast enough to get where you need to go, but enough to make you able to target another slanted wall that's even higher. Put a portal there and do the same for the other portal.

Now you have enough to reach the higher ledge.

To the boss
Now quickly go behind the turrets as they will be delivered to kill you, then take out the two turrets. Placing a portal under them works if you didn't manage to get behind them. Now you have to jump your way up a hole. Put a portal on where you will jump on the hole, and put another on the floor of the main room. Now jump on the portal and you may find that it is enough to build your way up the hole.

Now just aim yourself to the next platform and then follow a catwalk followed by some doors you just need to open.

GlaDOS
Now you get to battle the boss: GlaDOS.

After her talking, put the core near the incinerator, then portal to the room with the button. Put another portal near you. Pass through the portal and press the button. Quickly put the core in the incinerator.

GlaDOS explains that the core you just destroyed was a recent morality core that stops her from filling Aperture laboratories with neurotoxin and other deadly gasses. Within the six minutes GlaDOS contaminates the facility, you need to finish her off and dodge the rockets. The computer has the advantage, since you can't shoot her cores out with the portal gun.

However, you can redirect rockets back at the core. Shoot a portal to a wall, and a second portal that gives a direct line of fire between the turret and GlaDOS (the floor under GlaDOS is a good place for this portal). When you stand in front of the first portal, the turret should obtain a lock. Dodge the rocket, and it will hit GlaDOS.

The next core is on a pipe. Portal to the core and incinerate it. The following two cores are on the glass platform above, and in mid-air respectively. Torch them and win the game.