Rachel also picked out our excursion for this port - a Sail & Snorkel tour that we booked through Cruises Only.  Cruises Only is the Marriot Rewards (now Marriot Bonvoy) booking portal.  You get 6x rewards points when booking through them, and they offer excursions that are different from those offered through the cruise line.  We've booked excursions through Cruises Only many times, and what I like about them are that they typically have much smaller groups than those offered through the cruise line.  It's usually just our family of four and 1-2 other families.  It makes for a much more personalized experienced.  And they do guarantee that you'll make it back to the ship in time and reimburse you if for some reason the ship doesn't come into port (that happened to us last year in Jamaica).