Hey this Portal 2 game is really cool [yes, we already know that you all think!]. Some really good puzzles – not enough to totally frustrate you, but enough to make you sit and think for a few minutes. Most seem to have only one solution so far.
Story so far seems to be that I got back to where the evil robot was, swapped the core with the robot that had been helping me only for it to get all mean (or defensive) and throw me down a tube.
This ended me up at what is obviously a sort of 1960s era first version of the laboratory that I was in.