Other than going from the airport to the cruise terminal I have not had any experience with Puerto Rico.
I would appreciate some ideas on what may be fun for a day in San Juan. The group I'm with (10 people) are active with people from 22 - 65. The 65 year old is probably one of the most active and I'm probably the least active/mobile but I can do most things so hiking and other types of activities are fine. We all enjoy snorkeling, beaches, ziplines, ATV's and other more extreme activities. We all love good restaurants but prefer more out of the way places. No one is really into shopping other than a t-shirt or memory trinkets. I don't think any of us would mind a nice beach bar or a non-touristy bar to hang out in.
Any ideas would be great.