Melissani Cave was amazing, and was easily one of my top highlights of the trip. When we first found out we'd be going to Kefalonia, this was the first place I researched and placed on our "to-visit" list. I had looked at so many pictures before we went, and honestly they do not do it justice. I will say that it was much smaller than I had imagined, but it only added to the charm. Honestly the word that comes to mind when I take myself back to the cave is magical. The water is such an insane hue of blue, it basically glows. The sunlight pours in through the top and there's a slight mist that hangs just above the water, and it's all so beautiful.
The lake was discovered after a huge earthquake hit the island. The roof caved in, and residents found the gorgeous water. When you visit you can take a quite 10 minute boat tour. They take you around the perimeter of the lake, and then inside a dark cavern where the bats reside. If you dip your hand in the water, you realize how freezing it is. They don't allow people to swim in it anymore due to one too many accidents, but every once in a while they'll open it up for local residents.