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.
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.