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.
Devils Hole
Devils Hole is a geothermal pool within a limestone cavern in the Amargosa Desert in the Amargosa Valley of Nevada, east over the Amargosa Range and Funeral Mountains from Death Valley. Its waters are a near constant salinity and temperature (). The cavern is over deep and the bottom has never been mapped.
Devils Hole branches into deep caverns at least deep from an opening at the surface that is approximately . According to geologists, the caves were formed over 500,000 years ago. The pool has frequently experienced activity due to far away earthquakes in Japan, Indonesia and Chile, which have been likened to extremely small scale tsunamis.