You can get this achievement at any point in the game, it takes about 3-5 minutes. First you need to find a beach with acces to the ocean (It can be starting beach, north-east side of the map or near the town), then you just go to the deep water until giant tideworm eats you, you'll wash up on a beach and there is no penalty for doing so, repeat 10 times and you'll get the achievement!