Ride the Crocodile Trophy in Uncharted 3: Drake's Deception
Ride the Crocodile
Stand on the crocodile in the Secret Library
How to unlock Ride the CrocodileThis trophy is earned in Chapter 5 - London Underground.
Soon after you enter the library and watch a cutscene unfold, platform your way between the two central pillars in the room to trigger the entrance of a few bad guys. Once you have dealt with them you are free to leave the library through the opened doors the bad guys came through. Do so but immediately hang a right and go up the stairs to the upper floor of the library, and around to the opposite side to the entrance and stand beside the balcony. Facing out, vault over the balcony by pressing and you will hop over and land on a mounted crocodile. You don't have to stay standing, you can simply touch it on the way down and land on the ground floor again. Once you have done so the trophy will unlock.
Here's a video showing what to do, courtesy of PowerPyx: