This achievement requires you to beat the 14 challenge maps, and a further 6 advanced maps that were in the orange box version.
For a good video guide on how to beat the advanced maps go to:
http://www.portalwalkthroughs.com/For a written walkthrough (with pictures) of the challenge maps go to:
http://uk.guides.ign.com/guides/14266556/page_32.htmlThere does not seem to be one website containing a video walkthrough of the challenge maps, but sickder666 has many good videos of how to beat them on youtube, and i must say i have been using them thus far and i find them very helpful.
To view his videos go to
http://www.youtube.com/profile?user=Sickeder666&view=vid...