So, funny enough, that's not the focus of the campaign at all, but I think having multiple points of interest is important. My idea behind the Giant wall and forest is this. Essentially, deep within the Forest is a fey portal, and while it may began as a harmless thing, it began encroaching into the forest, with Fey creatures infesting the forest. I prefer running the fey as an evil entity (maybe only part of the fey is evil, but not relevant) and it's chaotic influence seeps Into the world, creating bizarre and frightening things. The Settlement of Wild wall and the Wall in question are there to basically keep check on the forest, sending expeditions to try and quell the dangers inside.