During the Wan Chai canal level (the area you need to pass through to get to Tonnochi road), you need to locate a bar called the Old China Hand. It's fairly hidden but easy to find if you simply explore the main pathway. The entrance will be down a couple flights of stairs. Upon entering, take an immediate right into the kitchen, then follow the path into the freezer. Climb the boxes in the freezer and get into the vents. Proceed until you reach a flooded tunnel. Turn left in the flooded tunnel and at the end of the tunnel you'll find a corpse with some great "treasure" and this achievement.