Бульк!

coords 4893/4910 Once u reach the coords which is by trees. When u look up at the waterfalls the coords are to a spot to the right of the waterfalls. When at the coords have ur toon face slightly SW and than jump or run off the cliff. As soon as u hit the water without hitting anything else u should get the achievement. Enjoy.

It worked for me! And if you want to walk very slow to the edge (behind the skeleton), just walk backwards!