Take the 2-minute tour ×  Amazingly I'm having trouble Googling
for this one and I don't have the time going through all the
chambers for crazy jumps etc...  Where is it?  share|improve
this question  1 Answer 1  up vote 8 down vote accepted  It's at
the end of the 9th Chamber of Course 4: Excursion Funnels.
Remember the part where you have to create a light bridge that
crosses in front of the turrets on the conveyor belt, and they
all just hit it one after the other and die? Normally you'd have
to move that light bridge slightly to the left so that you can
continue with the level.  Instead of moving the light bridge,
place the exit portal of your excursion funnel beside it - so
that you start moving backwards into the unexplored depths of
the level. You'll pass by the cube, which you'll be able to see
through the light bridge. Then you will die.  The achievement
should pop here automatically. Here's a video of the process.
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