It is completed on the final step of area 4, the best way to complete this is to get to the final room (where you find the CD) and then to kill yourself going back to the beginning as this removes all the turrets that may hinder your movements.
As soon as you approach the area shown the wall will open up and you will get the achievement (Note: You do not need to grab the cube, just see it).
First tutorial ish video upload of the achievement? I think so…
If you need any help with an achievement or would like a guide on how to do one, please contact me and we will try and get a video tutorial uploaded.
Portal 2 Co Op was completed by TeamFail Tayl0r and 0ni0ns after a few hours, we will be attempting a speed run at some point so stay tuned incase we do it.