The Italian island home to the Blue Grotto sea cave is Capri. Known locally as the Grotta Azzurra, the cave opens along Capri’s coast near Anacapri and is famous for the intense blue glow that fills its water and interior.
The color comes from sunlight entering through a submerged opening beneath the small cave entrance. Water filters out much of the red light, while blue light is reflected through the seawater and into the grotto. The effect is strongest when the sea is calm and visitors enter at suitable tide conditions.
The entrance is only about 2 meters wide and roughly 1 meter high at low tide. Visitors traditionally enter lying flat in small four-person rowing boats, guided by an oarsman using a chain fixed to the cave wall. Swimming in the grotto is prohibited, and rough seas can make entry unsafe.
The cave has ancient history as well as dramatic scenery. Roman remains, including statues of Neptune and Triton, indicate that it was used during the reign of Emperor Tiberius. German artist and writer August Kopisch helped bring the grotto to wider attention after visiting it in 1826.