Load (or progress to) Chapter 27. Should be a picture that has (from left to right) a ladder, box, a switch on a platform, and a big-ass cog/gear. Or refer to the picture below.
If you need assistant getting to that part of the level, watch the following movie, but don't pull the switch on the platform (or just stop following the video just before 2:00.)
(Credits to 'bewaretheb')
Instead of pulling the switch, jump from the platform that the switch is on, and jump to the edge of the cog, pulling yourself onto one of its teeth.
(Credits to 'gamerguides')
Step on the glowing egg on the last tooth and the trophy will pop.