The Blue Cave on Biševo Island sits 4.8 nautical miles southwest of Hvar, accessible only by small boat through a narrow coastal opening that admits sunlight for just three midday hours. Discovered by Baron Eugen von Ransonnet in 1884, the 24-metre-long sea grotto earned its name from the electric azure glow that occurs when morning sun refracts through an underwater aperture, illuminating the limestone ceiling and turning the water a spectral cobalt. The phenomenon is most vivid between late May and early September, when the Adriatic sun tracks high enough to penetrate the cave's submerged entrance at the optimal 42-degree angle. Blue Cave tours from Hvar depart between 08:00 and 18:00, though guides universally recommend the 10:30–13:00 window when refracted light reaches maximum intensity. Most speedboat operators bundle Biševo with a circuit of the Vis archipelago, stopping at Stiniva Cove, the Green Cave on Ravnik Island, and the village of Komiža. The 24-euro conservation fee—collected on arrival at Biševo—funds the Croatian Ministry of Culture's ongoing geological monitoring, which tracks sedimentation rates and water salinity to preserve the cave's optical clarity. Since 2019, daily visitor caps have been enforced during peak season to prevent propeller wash from stirring bottom sediment that dulls the signature blue. The cave's interior measures 16 metres wide at its broadest point, with water depth averaging 10 to 12 metres depending on tidal cycle. Visits last approximately 10 minutes, conducted aboard wooden rowboats that ferry groups of six from anchored speedboats outside the entrance. Photographers favor the brief moment when the boat passes directly beneath the refracted beam, a position that lasts roughly 40 seconds before oarsmen pivot toward the exit. The surrounding waters off Biševo support dense posidonia meadows and grouper populations, protected under Natura 2000 designation since 2013. Hvar's geographic position—equidistant from Split and Vis—makes it the primary embarkation point for Adriatic island circuits that combine natural landmarks with swimming stops. Speedboat tour itineraries typically allocate 90 minutes for the outbound crossing to Biševo, followed by sequential visits to four or five islands before returning to Hvar by late afternoon. The Blue Cave remains the anchor attraction, its entrance fees and boat transfer logistics unchanged since the conservation management plan took effect in 2018.