You can grab this easily by drowning. Open up the campaign tab, go to Aelion, choose a "Region". Any level will do, walk around within the open world until you find an ocean or body of water and jump in. This will kill you, the achievement will unlock.
Lanber Forest Directions, head straight out of the town and continue the path while keeping to the right. Head through a small little town of outlaws and continue down that road, there will be an ocean at the end of it.