Cenote
A cenote is “a deep sinkhole in limestone with a pool at the bottom that is found especially in Yucatán.”
A cenote is the result of collapsed limestone which exposes water beneath.
There are four classifications of cenotes; ancient, cavern, semi-open and open. The more open the cenote indicates how long ago it was formed.
Take caution when visiting a cenote as some are prone to caving into the water below and could possibly be fatal for explorers.
Side note: The ancient Maya used cenotes as a water source and sacrificial offerings.