The cave lake of Melissani is one of the most enchanting and well known attractions of Kefalonia as well as being a site of great historical interest. Located at Karavomilo, very near Sami, it was rediscovered in 1951 by famed Greek speleologist G. Petrocheilos and opened to the public following extensive access works. A large section of the cave roof has collapsed, allowing sunlight to filter through the overhead vegetation and giving the water a brilliant turquoise colour.

In antiquity the lake was a place of worship for the god Pan and the nymph Melissanthi. According to the myth, Melissanthi drowned herself in the lake over her unrequited love of Pan. Another version tells of a shepherdess called Melissanthi who accidentally fell into the lake and drowned while searching for a lost sheep. In the lake lies a small isle on which the archaeologist S. Marinatos discovered a shrine dedicated to Pan. The finds, which are now displayed at the Argostoli Archaeological Museum, include a clay figurine of Pan, a plate depicting dancing nymphs, a clay tablet depicting a procession of nymphs and a small tablet with a relief carving of a female figure.

The cave lake is the result of geological process called karstification, in which the limestone bedrock is dissolved by groundwater creating subterranean caverns. The existence of a karstic network across the island was proven in a 1963 experiment, in which green dye dumped into sinkholes on the other side of the island (Katavothres) resurfaced 14 days later in Melissani lake.

Today, visitors can take a guided tour of Melissani cave lake in small rowing boats and enjoy the magical spectacle of its stalactites and sunlit turquoise waters.