(just for the record, the fascinating human remains found in cenotes, including prehistoric human remains)
Sistema Sac Actun – longest underwater cave
"...the extensive cave systems under the Yucatan Peninsula have also been a guardian of hidden and invaluable treasures to learn from our history. Remains of Pleistocene animals and humans that date from a time long before the occupation by the Maya civilization have been found within submerged passages and galleries. Being underwater, these caves provide a unique environment for the preservation of human and animal remains...."
https://sites.northwestern.edu/monroyrios/sistema-sac-actun-en/