What the place needs
Start with somewhere walkable, with clear transport and people used to welcoming travelers. A mid-size city or a town with a square, a market, and one day trip usually works better than a huge circuit. If you get lost, it should be easy to get back to a point you know.
Pick a place where getting back to your stay does not take much thought. The adventure is what happens in between: the coffee, the conversation, the street that was not on the list. Not solving three train connections with your bag.