One of our sons married a wonderful young woman who is from Puerto Rico. Naturally we have the inside track on touring there. There is so much to see and do. Get a rental car and go to the rain forest as someone mentioned above. If I had to pick one thing that anyone can do and is memorable in San Juan, I would suggest the walking lunch tour of Old San Juan. We used this outfit and would recommend them to any friend:
http://www.sanjuanfoodtours.com/san-...d-tickets.html
They (and others) also do dinner tours. You can easily rent a condo and base yourself wherever that is. Our last trip we based in Fajardo (on the eastern end of the island) and loved it. We found a neat condo overlooking a marina on line. Regardless of what you do, you'll love it. P.R. is the best kept secret vacation spot!