Marta, Welcome to Cruise Chat! I am sure that you will get all kinds of recommends from the members shortly. You can also select the "Find" button with the magnifying glass (2nd blue line above your question) and ask about that and it will bring up lots of info..Or, you can go on the "Port Hotels" section and do a find there..
Old San Juan is a great place to spend some time touring prior to a cruise. Good Luck !