At the end of the first section of the level, you will see a tall tower. Go around to the back of it and hop in the whirlwind there. Once at the top, look down and to the left and you should see a platform with two green gems and a gold key. Glide down to it and grab the key.
From here, complete the level as you normally would. After you defeat Doctor Shemp, glide to the ledge just below the "Return Home" vortex and approach the strong chest there (The silver one with the lock) The key will unlock it and voila! Trophy unlocked, too.