The first time I visited the UK from Oz, I had my son and daughter with me (she was 18 and he was 21). I know she liked Camden Markets, and she also liked Covent Garden. Another good day out was Madame Tussauds and the London Planetarium, although I gather the Planetarium in the form that we saw it has been taken over by Tussauds now, and may not be as good as it was.