Happens for me in most Larian games because there's so much hidden stuff and you can go pretty much everywhere from the get go with different movement abilities. In my latest playthrough I haven't even been to the village with the windmill, however I have been in the Underdark. Nonlinear gameplay is a great strength of Larian.
How did you get into the Underdark without going into the goblin camp first? Is there an entrance somewhere else?
