I would advise to pre-book any excursions prior to arrival. Don't try to find them onshore. There's not much to do in Belize City -- you have to go to another location, by boat, bus or plane to get there. My cabin mate and another friend wound up booking the same Goff's Caye excursion available on the ship (for $20 less per person), but wound up standing on the pier for two hours due to the difference in local time and ship's time. They had an excellent time and saw a pod of dolphins, sea urchins, sea cucumbers and more.