Cave Into the Blue Cave. Soak your mind and body in the deep blue waters of the mysterious. Yet inviting Blue Cave on the island of Biševo. Mother Nature gave birth to a true wonder here, a wonder you’ll be able to see. We are grateful to our capable skippers who steer the small boats that are allowed to enter the cave. This cerulean oasis is unique because it’s formed due to seawater eroding limestone, a rock Biševo is composed of in its entirety. Thanks to the sunlight’s reflection off of the white seabed. Which creeps through the opening at the top of it, and a mesmerizing blue hue fills its capacity.