Melissani Cave

Melissani Cave also Melisani is a cave located on the island of Kefalonia, northwest of Sami, about 5 km (3.1 mi) Southeast of Agia Effimia, Northeast of Argostoli and Northwest of Poros.
In Greek mythology, Melissani was the Cave of the Nymphs. It features a lake surrounded with trees and forest, and is located east of the mountains of Evmorfia and Agia Dynati.
The lake’s bottom is covered with stones. Plants grow at the opening of the cave. The color of the stone near the opening is stucco to honey-like brown.
The cave was rediscovered in 1951 by Giannis Petrocheilos.
Source : Wikipedia 
The Cave of Melissani in Kefalonia: Situated just outside Sami, the Cave  has a strange appeal. It is one of the most significant places for tourists to visit in Greece. Surprisingly, there is a lake inside the cave that has trees and forests surrounding it. The cave itself is B-shaped with two chambers or halls separated with land or an island in the center. The roof of one of the halls caved in centuries ago letting sunlight filter in. The depth of the lake is 20 to 30 meters. When the sun is right overhead at noon, the sunlight hitting the turquoise-blue waters create a magical illusion and the whole Cave of Melissani suddenly feels lit with blue light.
Source : greeka.com 
https://www.youtube.com/watch?v=sZeMt5yavsM
https://www.youtube.com/watch?v=4bXX6irmVJs
Reviews
https://bit.ly/3l77rV3