Glaronissia

Glaronissia is a tiny uninhabited islet cluster off Milos's north coast composed entirely of hexagonal basalt columns — a geological spectacle that continues vertically beneath the surface, with columns dropping into clear blue water to 30 metres. The walls between the columns are carpeted in coralline algae and encrusting sponges, and large grouper patrol the base of the structure with territorial authority. The site feels genuinely prehistoric, and the contrast between the dark basalt and the azure Aegean water is one of Greece's most memorable underwater vistas.