A resident of Isla Mujeres told me that one of the things he loves about the island is that everyone is happy. And it’s a good point — with the warm sun and the beautiful blue Caribbean views in every direction, it’s hard not to be in a good mood. On top of the sunshine and scenery, the island also has an unquestionably relaxed vibe, full of visitors lounging by the beach and driving around in their golf carts. . . .