The achievement is located in chapter 6 called Ashes to ashes in the middle of this chapter.
After a while you come to a rocky outcrop where the first sign is. From here you must swing through the fire to the other end where the second sign is. Usually you swing from point to point with the sticks, you may not do that this time.
After jumping to the first lasso point, all you have to do is use RT and use the initial swing to get to the other end.