Chapter 2 Chamber 6. When you get to the button to release a cube when you first press it glados will drop a load of crap out of it including a radio needed for this trophy and a turret required for this-
move both your portals of the slopes at the far end of the chamber before pressing the button and the items dispensed will end up on the ledge where the 2 sloped light grey walls are. Go collect the radio and take it back to the start of the level via a portal. From there put one portal on the first slope you hit and the other portal high up and right at the far end on the wall to the left of the platform as you look at it. Now pick up the radio and jump on the first faith plate. You'll end up in a hidden office which is one of the rat man's dens. Trophy unlocked
There is also one other trophy on this level-
The Drop Box trophy in Portal 2 worth 42 pointsPlace a cube on a button without touching the cube