My wife and I went on our honeymoon last year to the Caribbean. We went with Royal Caribbean and were on the Voyager of the Seas. We both had a lot of fun and it was well worth the price. The cruise was 7-days long out of Miami and the ports of call were Labadee (Haiti), Ocho Rios (Jamaica), Georgetown (Grand Cayman), and Cozumel (Mexico).
If I were to do it over again, the only thing I would change would be to do less excursions. On Labadee, all we did was rent some snorkle gear and do that all day (which resulted in my pasty white ass being burnt the rest of the trip, but it was worth it). Apparently there are a couple plane wrecks in the water there and it was fun searching for them. That definitely was the best excursion of the trip.
On Ocho Rios, we did the touristy thing and went to Dunn's River Falls. It was ok, but I think next time we would probably stay at the local village next to the port and go to Margaritaville (using the money that we would spend on the excursion on liquid propulsion instead). Dunn's river falls is swamped with a shanty town of vendors, so be prepared to be hassled (or hustled depending on how you view it) if you go.
At Georgetown, we did the touristy thing again and swam with the stingrays. This was definitely the worst excursion. You have to get on an overcrowded boat and take a 30 minute trip to the sandbar where you are basically elbow-to-elbow with passengers from 20 other over-crowded boats. It was a very overrated excursion, and we probably could have found something better to do near the port. Unless you have some obsession with seeing stingrays up close, I doubt you would enjoy this "must see" excursion.
So, at Cozumel we finally wised up and just took a cab into the downtown area and spent some time shopping and getting drunk at Carlos and Charlies.
The best part of the cruise is the ship, so make sure you go on a nice one if you do go on a cruise. I would also recommend getting a room with a balcony, because we spent a lot more time in the room than we expected and it was very nice being able to sit out there and read a book while you watch the ocean go by. Go through a travel agent, because i guess it's pretty frequent that they will give you free (or cheap) upgrades. We originally booked an interior cabin, but we upgraded to a balcony for a very low price a few weeks later.
The food was excelllent, and you really only have to pay for drinks unless you are ok with water, juice and iced tea for the week (pop and alcohol are not included). All in all, compared to a regular vacation where you have to worry about car rental, hotel accomodations, food, entertainment, etc. a cruise is a good way to have it all planned for you so you can sit back, relax and enjoy the experience.
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One more thing I forgot to add. Be sure to go to the art auction on the cruise if they have one. You can usually get a pretty good deal on a painting and they usually have raffles too. When we went there were very few people there and we ended up winning a very nice painting. We also got a small piece for free just for going and we bought another fairly nice one for $80. There was never any pressure to buy anything and we got free champagne
