Blue Lagoon (Geothermal spa) in Iceland

The Blue Lagoon geothermal spa is one of the most visited attractions in Iceland. The spa is located in a lava field in GrindavĂ­k on the Reykjanes Peninsula, southwestern Iceland. The water temperature in the bathing and swimming area of the lagoon averages 37–39 °C (98–102 °F). [Wiki]