Kefalonia is a local-operator island, not a liveaboard destination. Divers plan around day boats from Fiskardo, Skala, Lassi, Lixouri, Agia Efimia, and nearby harbors, mixing clear-water reefs, caverns, walls, amphora fields, and the advanced HMS Perseus submarine wreck. Snorkelers get easy turquoise coves such as Emblissi, Foki, Antisamos, Koutsoupia, Spartia, and Skala, while freedivers can find calm training-friendly bays when wind and boat traffic are managed. Non-divers are unusually well served: Melissani and Drogarati caves, Mount Ainos National Park, Robola wineries, Assos, Myrtos, Argostoli turtle watching, and small-harbor dining can fill a whole itinerary. Late May to October is the main water season, with September and early October often the best balance of warm sea, softer crowds, and good operator access.