From Cancun in the north, 80 miles south to Tulm, is where Mexico's legendary Riviera Maya begins. Between Playa del Carmen and Tulm is Akumal, the Mayan name for the "Land of the Turtles." Akumal, which is well-known for its breathtakingly clean bay teeming with sea turtles, has developed from a secluded dive location to a burgeoning tourist destination and has turned into a viable business...