The Blue Grotto / Grotta Azzurra, is a sea cave on the coast of the island of Capri, southern Italy.
Sunlight shining through an underwater cavity is reflected back upward through the seawater below the cavern, giving the water a blue glow that illuminates the cavern.
The cave extends some 50 metres into the cliff at the surface, and is about 150 metres (490 ft) deep, with a sandy bottom.
Gioacchino La Pira | The Blue Grotto on Capri island
The Blue Grotto is one of several sea caves worldwide that is flooded with a brilliant blue or emerald light.
The quality and nature of the color in each is determined by its unique combination of depth, breadth, water clarity, and light source.