After logging on to ApertureScience.com, type ? or LIB to see the following list of commands.
Type DIR then type APPLY to take an application for entry into the "Enrichment Center".
While logged into the ApertureScience.com site, type THECAKEISALIE to access an interesting message left by some employees.
The graffiti in the game are clues for the web site. Go to the site and enter LOGIN as a command. Enter CJOHNSON as a username and TIER3 as a password. After logging in, type HELP for a list of commands.
In addition to logging in as "CJOHNSON" (Chell), you can login as anyone desired by typing a username longer than two characters and using PORTAL as a password.
On the level where you get the companion cube after you run past the energy balls and are in the room with the three elevators, there are two doors leading to a catcher, and a platform that is pushed out of the wall. Walk up to the platform that is pushed out. Crouch behind it and walk through the opening. On the left hand side are a group of pictures of people with boxes for heads and hearts around them.
At the end of the advanced map for Chamber 18, you will have the same raised platforms as you did in the normal one except now after you leave the lower one, it falls into the toxic water. This forces you to be more precise with your portal jumps. However, you can get past this easily. Do the platform jumping as usual, but if you miss just land on the platform you came out of. You should be able to fire an opposite color portal at the wall where you entered this area, allowing you to go back to the start. All the platforms rise again and the portal is still where you left it. You can now fall into the pit again and be able to portal jump to the next ledge. This take longer but does not require precise timing.
Start the game and wait for the voice to stop talking. Before you go through the first portal, take the radio on your table. Carry it with you until you get to the first elevator. Carry it through the particle field and it should get destroyed. Play until chamber four as usual. In chamber four, a radio should be dropped down through the tube with the box. It will end up lying in the pit. Leave it in that chamber, and do not destroy it. Play through chamber five for a strange surprise. Activate the two buttons and the door should open as normal. The radio will be sitting in the center of the floor in the next chamber.
 Enable the changelevel testchmb_a_02 code, then shoot both cameras. Repeat the process as many times as needed.