This trophy is earned for finding the thirteenth secret and can be found on Checkpoint 54
It can also be found in this video, with a text description of its location below
[13:58] - This takes place during the elevator puzzle. Get to the bottom of the shaft and bring the elevator to the top level. Now go grab the followers that are on top and have them follow you on the same level. Go into the elevator and close the door so that you create 2 groups of followers. Take the elevator down and the other group will be on top of the elevator. Take the elevator back up. Exit to the right, use group 1 to boost you to the yellow wire and climb it to the top. Now you'll be in the attic, and can use group 2 to boost you to the secret nearby.