Blue Hole (Castalia)
The Blue Hole is a fresh water pond located in Castalia, Erie County, Ohio, in the United States. From the 1920s to 1990 the Blue Hole was a tourist site, attracting 165,000 visitors annually at the height of its popularity, partly because of its location on State Route 269, about southwest of the Cedar Point amusement park in Sandusky, Ohio.
Great Blue Hole
On-shore caves of similar formation, as large collapsed sinkholes, are well known in Belize and in the Yucatán Peninsula, where they are known as "cenotes". Unlike the mainland cenotes which often link to underwater cave systems, there is little evidence of horizontal development in the Blue Hole.