In the Arctic Base, you will reach a lake with many floating ice islands and James makes a comment about a raft. Before you attempt to solve the puzzle of getting across, head up the slope to the right. At the top you will see a small stone doorway set into the rock face on the right.
Shoot the gold symbol above the door. This opens the door but starts the crusher trap. At the back, above the Path of Light treasure, is a gold diamond. You need to shoot this to disarm the trap, but you have to be quick and time your shot in between the crusher opening and closing. The achievement pops as the crusher grinds to a halt.