Before our cruise out of Dover, we purchased English heritage passes for overseas visitors and saw quite a few places in London, rented a car and visited as many sites as we could in the Dover area. It looks like there are some free sites to visit in the Southhampton area as well as a few that would be paid and could be part of the pass. We enjoyed all of the sites we went to and felt it was a nice historical balance with the fun aspect of the cruise.