Hi Buff,
Here's a little piece I did for my "Ask RSD" column in "Rodale's Scuba Diving":
"Cenotes ("say-NO-tays"); Spanish for "caverns") are collapsed openings in the caps of underground cave systems. These are largely limestone structures and mostly filled with fresh water, although some are fresh water on top and salt water below. At one time above ground, over centuries stalactites, stalagmites, columns, petrified trees and flows formed. When the land sunk below sea level, the systems flooded. The most popular cenote diving area seems to be in the Yucatan Peninsula of Mexico, primarily around Akumal. This area contains the world's largest known, and as yet not fully explored, marine cave system.
You do not need cavern/cave certification or any special equipment to dive these cenotes. Your DM will be so certified and dive fully rigged. You will get a brief orientation, dive the rule of thirds, and nearly always be within sight of an exit, even though sometimes it gets pretty far away and small looking. Viz is extraordinary, although there is almost no marine life. The cenotes you will dive are not easily silted, and dangerous areas are well marked and off limits. Some of the best are Temple of Doom, Room of Tears, Dos Ojos and Car Wash. Water temps are about 76 plus/minus 2 degrees, so take thermal protection. Non-divers can snorkel, free dive and lay back in some cool and inviting areas. One thing you should be aware of is the somewhat strenuous trip to many cenotes. The ride in can be rough, and you typically completely suit up, except for mask and fins, and then hike to a steep and sometimes crude ladder entry.
Dives shops in Playa del Carmen, Akumal and Puerto Aventuras can arrange things. If you are staying on Cozumel, most dive shops there can set up a day trip."
Hope this gets you started.
DocVikingo
