Portal/Chamber 05

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.

Walkthrough
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…"

- GLaDOS

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.

No Cheating SpeedRun in One Segment for Mere Mortals
This is the first chamber with significant opportunities for the skilled (but mortal) player to shave seconds from their speedrun. Like Chamber 03, there is no need to walk into the main room. You do have to walk some of the way to trigger the portals to open, but when you get to the doorway don't go through but place the blue portal just to the right of it and keep walking through the portal and out of the orange portal on 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). 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, back up through the portals and rotate left 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. If either of the throws fail, you'll have to jump down, fetch the cubes to the buttons and walk out. 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 move promptly forward. In fact, even this doesn't help because GLaDOS has to finish her recitation.