In Chapter 21: The Forearm Of Apollo, at the very end of the chapter, you will enter the "Screw Of Archimedes". You must use the Oath Stone Of Orkos on the pressure plates to activate the elevator. While on the elevator, stay away from the fire, and block all incoming attacks until you reach the top. Once you reach the top, there will be no more fire, and you take your time killing the enemies. After they have all been defeated, you will get the "Fireproof" trophy.