So I just arrived at what I assume is the last area of the game, but I know Souls games always have an optional area or two, like Ash Lake in Dark Souls 1. I've come across at least two so far (one of which was hidden). Before I proceed to the final boss I want to make sure I visit all the areas in the game, since I don't want to miss out on any content.
Are there any optional areas in the game? If so, how do you get to them?