Actun Tunichil Muknal was highlighted by the BBC recently. It's a great article explaining many facets of the cave, along with some of the Maya history of its use. They interview Hector Bol in the article. Definitely worth a read.
"In Belize's ATM Cave, details of ancient Maya religious sacrifices come into focus as new research creates a picture of how rituals were used to re-enact the Maya creation story."