We usually just wander around and do a little shopping and bar/restaurant hopping. Of course the forts are worth a visit. And the cematary adjacent to El Morro is interesting if that's your cup of tea - great setting and history. Overall though, I just love the ambiance of Old San Juan in general. We've never stayed in Old San Juan as we have kids who want the beach and a nice pool, but the El Convento seems like a great place to stay. The Puerto Rico area of the Trip Advisor forum is a great place to get information specific to San Juan - there are a lot of active and knowledgable contributors there.
