When in Goat MMO, you can hit
for a map of the area. You have to enter areas to "discover" them in MMO fashion, so use the map inside the spoiler for reference if you have not previously visited the mentioned locations in the following guide:
Begin in Goatshire near the center of the map, and head down the path on the west side of the river shown on your map.
At the end of the path, you will "discover" Bullgrurzh if you have not been there before, but you're actually standing on top of it. You will see a single large tree directly in front of you, and you want to look directly behind the tree for a hole in the ground. Simply hop in for your achievement.
You can exit the area you land in by either jumping off the edge or by restarting from the pause menu.