The Blue Hole is a cool and refreshing place for an afternoon swim. It was formed by the collapse of an underground limestone cave. In this case, the river running through the original cavern still flows through the cave system, and forms a sapphire-colored pool at the bottom of the sinkhole. The depression measures about 100 feet deep and 300 feet in diameter, with the actual blue hole at the depression’s base having a depth of about 25 feet.