A Cenote is a sinkhole with exposed rocky edges containing groundwater, above or beneath ground. It is typically found in the Yucatán Peninsula and some on nearby Caribbean islands. The term derives from a word used by the low-land Yucatec Maya to mean any location with accessible groundwater.
After the meteor impact in the Golf of Mexico 65 million years ago, the peninsula of Yucatan vanished under water for over 60 million years. In all this time the ocean washed the limestone under the peninsula out and is now full of tunnels and caves. The rainwater is filtering through the limestone and collecting in tunnels and caves as underground rivers and cenotes.