San Juan is not the best for laying on the beach. We were there in August - We took a Island tour with one of the taxi vans waiting - It was $10 a person - about hour and half. You can then get a view for what's out there. We then spent the rest of our day walking around the shopping area. We found a nice little place for some lunch.
There's the Barcardi rum factory tour, there's always Fort El Morro to visit, and there always the rain forrest tour. If you like to shop there's plenty of that to do also. You just may want walk around Old San Juan for a while and go back to the ship for lunch. It's really not a boring port to visit.
I have never really figured that out either, must be cheap for them to dock. I would suggest the excursions also. I did a post cruise rain forest once and was good. If you just want to go on a ride around and see the city get on their transit bus, cost 50 cents. Must have exact change in quarters. Walk to the left when leaving the pier, then up the street to the transit terminal will be on the right. Wait for the bus that says "Condado" will take you around the city, you can get off over at Condado and walk or go into the nice hotels and casinos. Ask them which bus back to the pier..another 50 cents. Is totally safe in day time. But must have exact change.
best thing i found to do in san juan was to pray that my taxi wouldnt fall apart and that our driver wouldn't kill us.
If you like historic architecture and churches go to old town... if after the taxi ride you need a drink, go to the bacardi tour.
We stayed at the caribe hilton before a cruise. The wyndam across the way, with the casino, after the cruise. Didn't want to go anywhere but to the ship or to the airport.
Personally i found the people rude and snobbish, getting service even at the airport was impossible. I couldnt wait to get to miami...expensive, rude (except at the resort where they are paid well to be nice), and the city area showed a dirty, poor place, falling apart and building at the same time. beggars selling water at traffic lights...not the place i want to tour.
We go on our next cruise in Dec from san juan i will do the above mentioned praying till i get to the ship and save my time and money for better islands.
We got stuck on the RCCL adventure in san juan because of a dockworker strike it was strange, the govenor was negoiating but no cabs or trucks were allowed in the port. Princess was behind us and must have used thier crew and paid some scabs because they unloaded while we sat...we didnt care because we got an extra 6 hours, with lunch, and didnt have a flight to catch. I hope they don't do that often because we didn't book a room this time.