For this achievement all you need to do is visit the old goat who lives in the mountain castle. The castle can be found by following the map north then cross the bridge on the west over the lake, then follow the path round by going left after the bridge and you will eventually find it. If you having trouble finding it look to the sky and there is a big red beam shooting into the sky. Once you are at the castle go in the entrance portal there is a path to follow be careful as the path is full of booby traps but don't worry to much as you can't die so they don't effect you to much. At the end of the path you will get into a large room where you will find The old goat
when you enter the room the achievement will pop.
If you would like a guide of how to find the castle or a video guide for the whole achievement I have included my video guide below