I went to the resort you are referring to. It is well outside of town. You need to pay the tour operators tncruieman refers to to get you there. I think it was $20 a head for the bus ride and entry. It was a really nice resort and worth $20. But hanging out right there on the free beach is nice too. And you can do the local culture thing if it suits you.
The reason I went to the resort is that my wife and a daughter wanted to do the horseback riding. That tour was combined with the beach break thing which happened to be at the same resort. So, the other daughter and I hung out at the local beach and got to meet up with the wife at the resort at the end of their tour. It would have cost as much for a cab ride and we wouldn't have gotten into the resort without paying. So all in all it worked well.
There is a free shuttlr bus from the ship. Take it. The same bus operators run the tours, so when you get into town and before you get off the bus, they will push their tours (probably a deal they run to provide the shuttle bus is they get to hawk their tours.)
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise, Magic 1/14
NCL Dream October 2006, RCCL Mariner OTS June 2007, Celebrity Silhouette 2013