The Emerald Grotto is one of the largest and most famous between the coastal grottos. It was discovered in 1932 and it measures 45 metres by 32 metres. Daylight filters through an entrance way which lies almost 12 metres underwater, causing it to refract and change colour, re-appearing as an intense emerald green inside the cavern. The changes in sea level over the years are evidenced by the columns of stalactites and stalagmites, some of which actually rise up out of the water.
Among the most important coelenterates to be found in the area is the rare Anemonactis mazely. This actinia usually hides from the light and lives buried in the sea bed, only coming out, cloaked in a bright pink colour, to mate during the winter months. The grotto can be reached by lifts from the road above or by a flight of steps with a spectacular view of the coastline by land. It can also be reached by sea by anchoring at the small quay in front of the entrance.