Get up starting at 4485,5050 and go generally east by north east to the pass at 4685,4980. Stand at 4840,4940 and run (do not walk, do not backup) off the cliff on a South West heading. Follow the line of the dead miners body. This is perpendicular to the line of the cliff face. This will carry you to the deepest part of the lake below.
You earn the title, "The Daredevil", for completing this achievement.