The cenotes at Chunkanan, also known as the Cuzamá cenotes, are a fabulous day trip excursion from Merida. Increasingly popular, these three cenotes (there are more but they are still difficult to access) involve a ride on a horse-drawn 'truck', a turn of the century form of henequen or sisal transportation along 9 kilometers of bumpy small rail tracks.
The success of this home-made tourist attraction has drawn the attention of the mayor of nearby Cuzamá, the larger town just before the Chunkanan hacienda. This fine fellow has decided that the cenotes are not benefiting his town and has made it his mission to stop tourists before they can get to Chunkanan, going as far as to use the local police at his disposition (who obviously have nothing better to do) to block the small road to the hacienda and divert tourists to 'his' truck people, thereby providing them with the tourism pesos and choking off the Chunkanan villagers who initially started the tours. Apparently police tell people that the hacienda is now 'closed' and that the tours originate in Cuzamá. Small town politics with small town minds.
I was just in Chunkanan two days ago with a group of nine people and it was a fabulous afternoon. The driver of the little truck said the conflict with the Cuzama people is ongoing - my suggestion is that you politely insist on going on to Chunkanan even if someone suggests that the the cenote route there is 'closed'.
Please note that there is some very slight wasp activity near the mouths of the cenotes for those allergic to wasp stings. This is common as the weather becomes hotter and the insects seek out out the cooler temperatures at the cenotes. We had one such person in our party but he was not stung.
Also, try to visit the cenotes on weekdays, preferably in the early afternoon; you may get the cenotes all to yourself. Avoid long weekends and holidays as the popular swimming holes can become quite crowded.
Word of warning: do NOT make the drive back to Merida from Chunkanan in the dark (we did). The narrow road accommodates only one and a half vehicles, with nasty potholes along the edges making for some interesting steel-nerve moments when approached by a bus or large truck and there is no where to go. Grit your teeth, hit those shoulders and potholes and pray for your drivers side mirror. Topes aka speed bumps, marked and unmarked, are par for this course as well.