Blue Cave (50 Shades of Blue), Balun, East side of the island of Biševo, Croatian Adriatic, Croatia

The Blue Grotto or Blue Cave (Croatian: Modra špilja), is a waterlogged 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. It is situated in the central Dalmatian archipelago, 5 km south-west of the island of Vis. 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.

First described and painted by Baron Eugen von Ransonet. It is also thanks to Baron Eugen von Ransonet that the cave entrance above the sea level was created in 1884 allowing small boats to enter it which ultimately gave rise to the popularity of the Blue Cave of Bisevo and more people started to visit the cave and it became a true competitor to the Blue Grotto (Grotta azzura) of Capri for the title of the most beautiful Cave in the World.

Before  1884, the only possible way to entrance to the Blue Cave of Bisevo island was through the underwater entrance which is the only natural entrance to the cave. It is not known who was the first who dived under and discovered the Blue Cave but it was thanks to Baron Eugen von Ransonet of Austria that the cave was first described, painted and presented to the general public to marvel upon.

The natural entrance to the cave, located on its southern side, is said to resemble a vault on the ceiling of a grotto. It is through this submarine-like opening on the ceiling of the cave that sunlight gets in and creates an iridescent blue glowing effect all around the cave. 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.

Depending on the season, the ideal moment to visit the cave is between 11 AM and 12 noon. At this time of day the sunlight reflects through the water coming from the white floor of the cave and bathes the grotto in aquamarine light, while objects in the water appear to be silver. The Blue Grotto (Italian: Grotta Azzurra) on the island of Capri in Italy is also famous for this type of phenomenon.

The cave receives more than 10,000 tourist visits every year. Blue Cave is at the top of the tourist attraction point of this part of Adriatic and tourist boats often include a visit to another similar cave on the island, the Zelena špilja (English: The Green Grotto), which is bigger in size and appears to be of an emerald-green tone due to a similar effect. 

The cave is made out of two chambers divided by the stone bar visible just below the sea surface. The entire cave is around 25 meters long with the cave ceiling towering some 15 meters above you. The sea depth of the cave varies from 10 to 12 meters depending on the position. Even though it is considerably deep, the silver reflection of the sea bottom makes it look as the cave is much more shallow. While the entrance to it measures 1.5 metres high and 2.5 metres wide.

As you circle around the cave and listen to the stories told by the tour guide you will exit the cave on the same place you have entered it with the feeling of awe and happiness you were lucky enough to experience the beauty nature decided to create just off of Vis island.

The first stop of the Blue Cave tour from Split is a distant island called Biševo whose popularity is mostly due to the presence of the Blue Cave it hides beneath the lime stone rocks forming this small island. Blue Cave,Blue Grotto or as it is locally called Modra Špilja is a Croatian Natural wonder for a good reason. It takes 1,5 hrs to get to Blue Cave from Split or Trogir by speedboat and about an hour from Hvar. The closest more inhabited place from where you could reach the Blue Cave with a taxi boat is Komiža town on Vis island, some 15 minutes by speedboat.