We were in the same boat after cruising from San Juan and took a post excursion through Royal Caribbean. They took us to one of the forts, then a shopping stop and a ride through New San Juan as well. Tour ended at the airport, so it worked out great and sure beat spending hours at the airport with no where to sit. For some reason, all the flights out of San Juan are later in the day. They also have tours where you can relax at a hotel before going to the airport, depending on how much time you have. They will let you know about these excursions once you are onboard. We had also purchased the transfers through them, and after we signed up for the excursion, they gave us a credit for the amount of the transfer, so that was also nice.