Try cenote (cave diving). This is a wonderful place for cave dives. Huge limestone caverns full of fossils. You can contact "Manta Divers" and a "Life Certified" guide will take you to places off the beaten track. One I recommend is "Tazimalzal". Visibility +100 ft, water temp 75°, depth 40-50 ft. Outstanding experience.
http://mantadivers.com
Have fun.