Blue Hole (Big Pine Key)
The Blue Hole is an attraction on the island of Big Pine Key in the Florida Keys. It is an abandoned rock quarry that was used for nearby road fills and Henry Flagler's Overseas Railroad. The water it contains is mostly fresh and is used by various wildlife in the area, such as birds, snakes, alligators, key deer and green iguanas. It is part of the National Key Deer Refuge.
Castalian Spring
In Castalia, Ohio, named after the famed site, the Blue Hole limestone configurations were tourist attractions for many years and are now fish hatcheries. Waters in the blue holes are of a constant temperature and never freeze over despite northern Ohio's cold temperatures. The water which averages 30,000 gallons an hour was first used to supply a local mill.