For this achievement all you need to do is Jump into the boat found in Twistram. Twistram can be found by following the map north from spawn and you will find it near the sea, The Boat can be found in the far right behind a building and all you need to do is jump into the boat and the achievement will pop
If you would like a guide of how to find Twistram or a video guide for the whole achievement I have included my guide below