The Blue Cave, Biševo

The Blue Cave, or Modra špilja, on the little island of Biševo off the outer Dalmatian island of Vis, is one of the Adriatic's natural marvels. It is a sea cave with a small entrance above the water and a second, larger opening below the surface, and around the middle of the day, when the sun is high, its light enters through that underwater window and reflects up off the white seabed, flooding the whole chamber with an unearthly glowing blue light while objects in the water shimmer silver. Visitors are ferried in on small boats through the low entrance to drift for a few minutes inside the glowing cave, an experience often compared to the famous Blue Grotto of Capri. Because it depends entirely on the sun and calm seas, and on transferring into small boats, access is tightly organised and weather-dependent, usually as part of a longer boat excursion around Vis and Biševo that also takes in remote beaches and coves.

What you actually see

• The glowing blue chamber - the cave lit ethereal blue by sunlight from below, around midday.
• The boat transfer in - the passage through the low cave entrance by small boat.
• Biševo's coves - the remote beaches and clear water around the tiny island.
• The island of Vis - the unspoilt outer island the trips set out from.

When to go

May to September, when the seas are calmest and tours run; the blue effect is strongest around late morning to early afternoon when the sun is high, so trips are timed for that window. Calm weather is essential, as any swell closes the cave. Peak summer is busiest, with queues of boats waiting to enter.

Honest expectations

Everything depends on sun and sea: the blue glow only appears around midday in bright weather, and any swell closes the cave entirely, so trips can be cancelled or fail to deliver the effect. In peak season boats queue to enter and your time inside is just a few minutes. It is a long way out, needing a ferry to Vis and then a boat, so it is a commitment. When conditions align, though, it is genuinely magical.

Nearby

The island of Vis with its coves and the town of Komiža is the base; Hvar and Split lie back towards the mainland.