We walked from our cruise ship as we got side tracked by the tourist shops in the port and missed the shuttle start point. We didn't have much idea of what we wanted to see so just strolled around. Make sure that you go to the viewing platform for a fantastic view and St.Nicholas (no longer a church and has toilets) which has some very interesting artefacts including some advice to princes and priests of their limited time on this earth....not for the squeamish.
When people say cobbled streets read boulders. There is nothing regular about these stones and very hard going in places.