It’s hard to believe one could make a bad choice of sights, looks like jimtorr has a bunch of great suggestions from firsthand experience.
I’d spend a day at the Tate Gallery, and visit the British Museum, also hit a couple of ancestral towns just to see what they’ve been up to since we left. ;^)
I’d probably want to see Hadrian’s Wall, but wouldn’t mind hiking along the Wansdyke, and/or so-called Offa’s Dyke, y’know, if I had a lot of time.
http://hadrianswallcountry.co.uk/
Good friend of Henry VIII lived here, got his head chopped off, you guessed it, by Henry ViII:
http://www.newton-cross.uk/carew-caste/
Tintagel, new find:
http://www.freerepublic.com/focus/chat/3663986/posts
And sometimes you may just want to enjoy some shopping, let’s say you like books:
http://www.google.com/search?q=Town+in+wales+outdoor+bookstores
Thank you. Those all look fascinating.