FREE DIVING In the deep waters of the Mexican Caribbean, you will be put to test. And you will be forced to appreciate the air your body craves. Take a deep breath, and dive at least 400 ft, the equivalent of a 40-storey skyscraper. Beware of the blood surge and the consequent blackouts on your way back to the surface, though: Of about 5,000 free-divers worldwide, an estimated 100 die every year