The Bath thermae spa is out of this world - well worth the brass. They did a sort of friday-night cheap package that included a meal last year, don't know if that's still the case, but just floating in the hot rooftop pool under the sunset has got to be the best experience ever. There is also a pool with racing currents that the kids will love. The Bath roman baths museum is excellent, with those narration hand sets with people like Bill bryson doing the talking. Shops are lovely despite the council's best efforts to wreck the town centre.
If you are in bristol the Banksy exhibition at the museum is free - get a bus up the hill as it's a b of a climb - even without Banksy there's loads to see in the museum.