A prehistoric spring inside a collapsed limestone dome, entered down a staircase, where a beam of daylight falls into clear…A prehistoric spring inside a collapsed limestone dome, entered down a staircase, where a beam of daylight falls into clear blue water over ancient rock. Ginnie Springs nearby offers the Ballroom cavern, glass-clear water and a fossil record, extinct mastodon and early human remains have been recovered from these springs. Named for the steam that rises from the opening on cold mornings, which early settlers thought looked like a chimney to hell. The Florida aquifer springs are among the richest Pleistocene fossil sites in North America, and Ginnie's cave system was where much of modern cave-diving technique was developed by Sheck Exley in the 1970s. Anchorage: Inland, a road excursion from a Gulf or St Johns River cruise. Hazards: No site-specific hazards noted, brief normally. Plus