Hello a good group to join is the U3A, i am not 100% sure if there is a group in Cadiz but i am sure there will be one locally if you have a look in the internet. Not sure if you have heard on U3A before but they offer a wide group of different clubs so there will always be a group within the U3A that will intrest you.
I would also suggest looking in your local expat newspaper, which i think the one to look in would be the Olive Press as they may be a page on different clubs and groups.
Hope you find what you are looking for.
Regards Cherie