“Blue Cave” is a name shared by sea caves in Greece, so the map pin needs a geographic reading. The Aerial listing places this one in the Sporades, and local Alonissos dive operators identify a Blue Cave off that island. It is not the better-known cave at Kastellorizo in the southeastern Aegean. That distinction matters when arranging a boat or dive: the island, launch point and local conditions are different.
The cave’s best-known visual effect comes from reflected light. A Greek-language dive operator describes turquoise water casting blue-green tones onto the rock roof, changing the view as a boat or diver approaches the entrance. This is a play of water, light and stone rather than a fixed color display. The effect depends on conditions, so photographs cannot guarantee what a visitor will see on a particular day.