Hello Diveray, regards to all.
Cenotes are pretty much (remember that they are underground rivers) with an overhead (like a dome in some areas) space where the trapped air gathers on top. Not a cave per se, more of a cavern. Your guide is fully cave certified, you don’t have to be but some people find it useful if they had some previous training. When I did Cenote Chikin Ha "The Western Water" in Puerto Morelos, up the road from Playa, I went to 38 ft. and in Dos Ojos and Batcave, 24 and 29 ft. accordingly. Hope this helps some. Dive safe, stay hard. Diver away!!!