Above is a video of Journey Mexico President, Zachary Rabinor, jumping into one of the private cenotes featured in many of their trips to the Yucatan Peninsula.
http://journeymexico.com/index.php/experiences/waterfalls_rivers_cenotes
Well this is really frigging crazy and I wouldn't recommend it, if you don't know what your doing, this guy obviously does though. I have always wanted to go see the cenotes and swim in them, since I first read about them in 1990, I hope that Angel and I will make it sometime soon.
You do have to climb a long way down into them though, and the thing that makes me nervous, what if your too tired to climb back up, specially with a kid...so maybe we have to wait a bit for a reason.
Looks fabulous! My niece got to go with her family, they got some great pics. Projecting and praying we will go sometime soon too!