I just got back from a cruise that went to those ports.
FYI. . Gr. Cayman and Belize are tender ports. in Belize, you'll have a 15-20 min tender ride as the ships have to anchor 5 miles off shore.
Isla Roatan: There is not much near the pier in this port. There is a "main" street with a number of little shops and things. It can get VERY hot and humid there, so walking a lot might be uncomfortable. I recommend doing an excursion. . .Fellow cruisers who did the zipline loved it. I didn't see a public beach anywhere hear the pier.
BELIZE: The port here is much better, with a lot of little shops. However, there is not much more to do, so I'd suggest that you do an excursion. Cave tubing is VERY popular. There's another thread that addresses this issue.
Costa Maya: The pier is built up (done by the cruise ship companies, actually) and has a swimming pool in the middle of the shopping area. There is a beach right there, too, although it is not a premier site. A suggestion is going to the fishing village of Mahajual. You can shop there and buy for less. Our bus ride to the snorkel site took a good 40-45 minutes.
Hope this helps.
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