Chamber 12

Place your first portal on the wall where the beam hits the wall. Look for the wall panel to your left, between the power receptor and the monitor, with four mini blocks on either side. Set your second portal here so the beam hits the receptor on the other side of the chamber.

Wait for the moving platform to reach the wall on the far left-hand side of the room and set a portal on that wall so it overlooks the platform. Step through the portals to be on top of the platform.

Position yourself on the far right-hand side of the platform and reposition the portals to power up the platform again.

Once moving, zoom in and place your crosshairs at the highest wall panel, directly above the portal aiming the beam at the receptor below. This will remove the killer laser beam field on your immediate left.

With the beam field removed, walk to the far left side of the platform and reposition the lower portal to power up the platform again. Jump off to the button just below you and wait for the platform to arrive back at the wall at the far end of the room.

Once the platform reaches the wall, remove the portal directing the beam to the receptor and place it on the far right-hand wall, shutting it down. Hit the button, and a Displacement Cube will drop onto the platform.

Turn to your immediate left and fire a portal here so you can step through onto the platform with the Displacement Cube. Repeat the steps to get moving, remembering to stop the laser beams as the platform is just over halfway through.

Once the platform is closer to the left side, stop it and position the Cube just in front of you. Get a portal on the laser beam and then one directly in front of you so it's hitting the Cube. Direct the beam to power up the receptor positioned just above the exit.

Set the cube down and jump back down to the platform below. Set up a portal near the exit and on a nearby wall, and walk through. Reposition the portals so the beam powers up the exit, and walk until you have to jump into the transportation beam.

Follow the metal walkways until you drop into the room and the screen fades to black.