Melissani Cave or Melissani Lake, also Melisani is a cave located on the island of Kefalonia, northwest of Sami, about 5 km SE of Agia Efthymia, NE of Argostoli and NW of Poros. The Ionian Sea lies to the east with the Strait of Ithaca. Forests surrounds the cave and the mountain slope is to the west. Near the cave is the entry to the cave with parking lots and is passed almost in the middle of the main road linking Sami and Agia Efimia especially to the northern part of the island.
Melissani cave is a typical feature of karst environment in coastal carbonate aquifer. It forms a kind of "cenote" as described in the Yucatan peninsula (Mexico). The vertical shaft gives access to the water table . This groundwater is brackish, mixing between fresh water recharge inland and sea water intruded in depth in the island. Huge karst conduits have been explored by speleo-divers. The bay of Sami has many cenotes, with impressive shafts, that have been inventoried in a GIS Database. The brackish water flowing through the cenotes outflows along the sea shore, forming brackish coastal and submarine springs. The groundwater of Melissani cave outflows at the "Fridi" beach. This brackish water is part of a famous hydro-geological phenomena : seawater is sucked in the west part of the island of Kefalonia, near Argotoli, and expelled in the bay of Sami.In Argostoli, the seawater flows into sinkholes, named katavothres, where water mill turns.