The Blue Grotto or Blue Cave (Croatian: Modra špilja), is a flooded sea cave located in a small bay called Balun (Ball in the local dialect), on the east side of the island of Biševo and about 4.5 nautical miles (8.3 km) from Komiža, in the Croatian Adriatic.

The grotto is one of the best known natural beauty spots on the Adriatic and a popular show cave because of the glowing blue light that appears at certain times of day.

[1] First described and painted by Baron Eugen von Ransonet, the cave was originally accessible only by diving as it had one natural entrance below the sea level.

As well, a stone bar, connecting two walls of the cave, is clearly visible just below the waterline, both in above-water photographs and in underwater photos.

[4] The Blue Grotto (Italian: Grotta Azzurra) on the island of Capri in Italy is also famous for this type of phenomenon.