- Above the doorway next to the chamber number.
- Above and to the left of the first exit door.
- In the final section with the ceiling portal.
This chamber is the first real puzzle of the game. It consists of a single door to the chamberlock, but for the door to open, two buttons need to be pressed. One cube is down in a pit as with the last chamber, while another is on top of one of two platforms. On the other platform is a fixed orange end of a portal.
Fire the portal gun down into the pit, then walk into the pit (Portal does not have falling damage, for good reason, and this is also why Chell is wearing "long fall boots") and pick up the first cube. Return through the portal to the platform, walk down to the main area, and place the cube on a button.
To retrieve the second cube from the second platform, re-create a blue portal anywhere reachable to get back onto the platform with the orange portal. Then fire the portal gun at the wall behind the second cube. Go through the orange portal, and walk back down to the main area with the second cube. Placing it on the second button results in the door opening.
However, before you can proceed to the next level, you must hear one of the many amusing lines GLaDOS utters throughout the game, contradicting the statement made at the end of the previous chamber:
As part of a required test protocol our previous statement suggesting that we would not monitor this chamber was an outright fabrication. Good job. As part of a required test protocol, we will stop enhancing the truth in 3…2…
Static once more subsumes the announcement.
To reach the chamberlock – which is on a floor above you – you need to notice that there's a fixed orange portal end in the ceiling above the chamberlock. Simply create a portal in the wall next to you, and walk through it to fall down next to the chamberlock. Whenever you go through a re-orienting portal in this manner, you will always land feet-first.
This is the first chamber with significant opportunities for the skilled (but mortal) player to shave time from their speedrun. As in Chamber 03, there is no need to walk out into the main room. Go forward out of the chamber lock and turn to the right as soon as you can. Place the blue portal on the wall to the right of the doorway. Continue moving forwards, but slide a little to the left, towards the opening, before you head directly for your blue portal. If you stay too far to the right, you will miss the trigger and the portals will not open. Walk into the blue portal and out of the orange portal onto one of the platforms. Once there, don't waste time going into the pit for the cube. Place the blue portal under the cube and it will fall out of the orange portal and hit you on the back of the head. Be ready for this, catch the cube and throw it onto the nearest button (but see below if you miss or can't throw cubes). Now, place the blue portal directly behind the cube on the other platform. Turn, go through the orange portal, out of the blue one, pick up the cube and throw it onto the other button. As soon as the cube leaves your hands, go back through the portals and turn so that you can see the exit doorway. If both throws were successful, the door will be open. Place the blue portal on the floor of the room beyond and go through the orange portal to pop up in that room, saving an awful lot of walking. The portal will close as the orange portal changes position. Immediately replace the blue portal under your feet, wait until you fall through and proceed to the exit chamberlock.
If either of the throws fail, you'll have to jump down, fetch the cubes to the buttons and walk through the door into the second room. If you've a reasonable chance of making the throws it's worth trying because failure is not too expensive. If you can't throw worth a damn, however, then don't plan to and just practice getting the cubes near the buttons as quickly as possible. Once you're into the second room, there's nothing you can do but place the blue portal under your feet and move promptly forward after you fall through. In fact, even this doesn't help with the total time because GLaDOS has to finish her recitation before the level ends.
If you throw both cubes and get them both on their buttons, you should be in the exit chamberlock within twenty five seconds from when the entry chamberlock door opens. Without the throws, expect a significantly longer time because of the walking. After placing the cubes on the buttons, you might try portaling back up onto the platform and then into the second room to improve your time.