[No Spoilers] I feel like Harrenhal should have a town inside.
It's described as the largest castle ever built, so it definitely has the space inside to fit a town or even just a village. It makes logical sense as well, the Riverlands is constantly raveged by war, and I'd bet that the average smallfolk would rather live inside the walls of Harrenhal than out in an exposed village. It's at the crossroads of Westeros as well so it's not like it's some place far out of the way that no one would want to live. I can see how people wouldn't want to live there because they think it's haunted, however I find it hard to believe that no one at all would be willing to move there if given the opportunity. If anything the Lord/Lady of Harrenhal should promote this as well, because if there is people living inside that they can tax, then that would help fund the upkeep of the huge castle. I know George isn't the best at working out the economics and logistics of his worldbuilding, but I just feel like this is such a missed opportunity to have a small town inside these giant oversized ruins of a castle.