It is a non-linear map which have many paths to take and reach the end. The point is, that you play a map one time and you are happy. Then you have a little break in Portal, because there aren't any new released maps for some time. But the answer is here: play the Deja-Vu again, but choose a different path with different puzzles. You can choose freely the way that is going to lead you to the end. Thats it!
random
I like this room
Damn! It must be like 200 degrees in that room! What with all the computers and all D:
No, it's 4000 degrees kelvin
Verynice, BTW whos that person in the tube?