Bath was a very nice place to base ourselves for a while and we delved into a lot of it, mostly by foot, and then ranged out and about to some castles (ruins and lived in) around the place as well. Of course, the Roman baths was fascinating (well worth the entry fee).

The village at St Michael's Mount where that castle is doesn't cost anything to go to but it's £16 ($33AUD) per adult to get into the castle. Some of it is closed off as it's lived in but most is open and it's incredibly interesting. The view off the top is excellent and it's amazing to read all the stuff about the history and all.