I think I know the place you are talking about. I got confused there and the moonlight area at first. Both are linked to finishing questlines first.
I agree though. It gets very confusing when you can or can't go to the next area. It gets a bit more confusing in the town where certain doors only are able to be entered. I think there needs to be something just to indicate when you can go into an area (just something simple like an arrow above the player's head)