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.
Santa Rosa, New Mexico
Santa Rosa has many natural lakes, an anomaly in the dry desert climate surrounding it. These are sinkholes that form in the limestone bedrock of the area and fill with water, and thus the lakes are connected by a network of underground, water-filled tunnels. The most famous of these is Blue Hole, a popular spot for diving, where cool water forms a lake over deep.