Anyone know of any good holiday resorts that can cater for a wheelchair user?

We have a friend who we have never been on holiday with, mainly because he is a wheelchair user and we didn't know how it would work. We would like to try and organise a holiday this year that he could join us on so we are looking for a place that caters for wheelchair users. We want to stay within Europe if possible and need somewhere that is mainly on flat ground. Also with a pool that has a ramp if possible. If anyone has any links or recommendations please let me know. Thanks guys!