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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 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-created the first portal to get back onto the first platform, then fire the portal gun at the wall behind the second platform. Go through the resulting portal to the second platform, 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 required test protocol our previous statement suggesting that we would not monitor this chamber was an outright fabrication. Good job. As part of 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.