Certainly the most famous and evocative in the world, for fame and suggestiveness, stands out the Blue Grotto, which is a natural cavity of about 1,500 square meters, accessed through a very narrow passage. Upon entering, it appears almost completely dark, but as soon as the eye adjusts to that light, it feels like entering a blue and transparent cloud, suspended between sky and earth. The blue color of the cave is an incredible effect called "refraction." This effect is determined by sunlight that, through a submerged opening under the entrance arch, is filtered, allowing only intense blue to pass through, astonishing tens of millions of visitors for about two hundred years, some of whom have even swum inside. 

Swimming in the Blue Grotto, according to those who have realized this dream, is undoubtedly one of the most beautiful experiences one can have. Many people wait until evening when the small boats leave, to be free to swim and enjoy such incomparable beauty.