The lake, located in a cave, was known in ancient times. The cave itself is B-shaped with two chambers or halls separated with land or an island in the center. The roof of one of the halls caved in centuries ago letting sunlight filter in. The depth of the lake is 20 to 30 meters. When the sun is right overhead at noon, the sunlight hitting the turquoise-blue waters create a magical illusion and the whole Cave of Melissani suddenly feels lit with blue light.