This is the fifth advanced chamber of the game. This version is unlocked when the original Test Chamber 17 has been completed. It has the extra challenge of replacing the Companion Cube with a spherical replacement, harder directing of the Pellets into Pellet catchers, as well as an extra flinging section near the end.
First to climb up to where the high energy pellets are, after collecting your sphere, use the sphere as a stool to jump up.
Then as the high energy pellet is coming towards you walk towards it so that the cube blocks the pellet and bounces off. Keep walking until you reach the next high energy pellet release mechanism.
Repeat the last step here but walk backwards so that the pellet is moving the same direction as you but will still collide with your sphere. Alternatively you can time it so that the pellet is heading towards you while facing forwards but the Pellet may get destroyed, with the new Pellet being released behind you (killing Chell).
As you exit the hallways of pellets place a portal on the portal block that the last pellet is colliding with. Then turn so you can see the two slanted land formations with glass in the centre. To the left of the glass on the ceiling place the other portal so the Pellet bounces off the slanted land and under the glass, into the Pellet Catcher.
Then turn left and walk into the room with the Pellet moving back and forth. Then crouch under the sphere to bounce the Pellet over the glass and into the Pellet catcher. This may take a few tries but you just need to get the right angle.
Now put the sphere on one of the buttons in the room the behind the glass pane from earlier. Then use portals to assess the strange secret room full of Doug Rattman's scribblings and steal two security cameras from it. Use the cameras as a stool to climb up on the other button.
Once you have established you can open both doors with the sphere and Chell, turn out of the room and portal back up to the hallways of Pellets. Walk down the one that you already stole the Pellet from and put a portal where the other Pellet collides.
Now place the other portal so that the Pellet passes under the pane of glass. Climb onto the button and watch as the Pellet activates the other Pellet Catcher.
Now that they are all raised portal on the first raised platform and jump along them and then jump to the left to enter a new room that wasn't accessible before.
Then climb the stairs with the sphere in hand to enter the room. Use gravity transferring through portals so that you and your sphere perfectly fly though the hole.
Now portal out of the pit you are in and walk to the next room.
Then put the sphere on the button to open the door that leads to a button on a stand. Press this button to activate the incinerator. Drop the sphere into the incinerator and exit the chamber into the elevator.
