- Above the main window.
- At the end of the stairway section.
- In the beginning entranceway. Go through a blue portal so you are standing in front of the orange portal. Shoot a blue portal over the wall back near the first doorway, then go back through the orange portal.
This chamber introduces you to the portal gun, and gives you the ability to create the blue end of portals — but not yet the ability to create both ends.
You start off with an overview of the chamber through a window. In the middle of the chamber is a portal gun, rotating and creating portals. Your first objective is to get the portal gun, and doing that requires waiting for the portal to be in the right place.
Go down the stairs to the right, and wait until a portal appears, then go through it. This will take you to the ledge opposite where you first were, but you can't proceed to the chamberlock, as the door to it is closed. Walk off the ledge into the main area of the chamber, and pick up the portal gun.
You'll notice that the orange end of the portal is permanently in place on the ledge you were just on, and you can use this to your advantage. Now that you have picked up the portal gun, the door to the chamberlock has opened, so fire the portal gun at any wall you can reach to create a portal between this level of the chamber and the ledge, then walk through the portal to get back onto the ledge. You can now proceed to the chamberlock.
There's nothing you can do to bypass or finesse anything in this chamber, so just make sure not to waste any time. The instant that the blue portal lets you through, go directly towards the Portal Gun on its stand and jump to land almost on top of it, but slightly to the right. The instant that the gun is in your hand, place the blue portal on the floor, just slightly ahead and clear of the base of the stand. Without pausing, fall through this portal to emerge back on the ledge. Immediately and, again, without pausing, turn to the right and go through the door to the chamberlock. Practice this and get it into muscle memory so that you can execute flawlessly in your speedrun. You should be in the exit chamberlock within 36 seconds from when the entry chamberlock door opens. You will have spent more than half of this time waiting for the round door to open.