San Juan is an easy port to just walk around Old San Juan. There are hills, but nothing that I couldn't handle (asthma, arthritis). We walked to Barrachina where the Pina Colada was invented (and, of course, ordered one). The Coach outlet was near Barrachina so we bought a couple of items there.
We saw Fairview House and garden, Romney Manor and a Picturesque stop overlooking the Ocean and Sea. Romney Manor's grounds were pretty and there is interesting history, but you have to stop at the Batik store and listen to the demonstration on how Batik is made and then walk through the store before going outside to see the grounds. At the Overlook - the view was magnificent, but there was distraction of people with their monkeys trying to see you pictures.
We love St. Maarten. We have been there several times and do not take excursions - no need to unless you want to. We take a cab to Orient Beach (the non-nude side). Cabs charge based on the number of persons and are easy to get at the port. We then took a cab into Phillipsburg, walked around, had some lunch at a French sandwich shop, then took the water taxi back to the ship.