Some say blue is a calming, relaxing color, so naturally, the Blue Grotto, or Grotta Azzurra, is a destination people seek to find beauty and peace. Visitors to the grotto can take a rowboat through it to experience the glowing blue waters, and the best time to do so is between noon and 2 p.m.
It’ll only cost you about $16 per adult to experience this phenomenon, which occurs because there is an underwater opening in the cavern where sunlight peeks through, illuminating the water. This glowing blue water is something that has to be seen to be believed.
The Blue Grotto is one of several sea caves, worldwide, that is flooded with a brilliant blue or emerald light. The quality and nature of the colour in each cave is determined by the particular lighting conditions in that particular cave.
In the case of the Blue Grotto, the light comes from two sources. One is a small hole in the cave wall, precisely at the waterline, that is a meter and half in diameter. This hole is barely large enough to admit a tiny rowboat, and is used as the entranceway.
In photographs taken from within the cave, the above-water half of this hole appears as a spot of brilliant white light. The second source of light is a second hole, with a surface area about ten times as large as the first, which lies directly below the entranceway, separated from it by a bar of rock between one and two meters thick.
Much less light, per square meter, is able to enter through the lower opening, but its large size ensures that it is, in practice, the primary source of light.
As light passes through the water into the cave, red reflections are filtered out and only blue light enters the cave. Objects placed in the water of the grotto famously appear silver.
This is caused by tiny bubbles, which cover the outside of the object when they are placed underwater. The bubbles cause the light to refract differently than it does from the surrounding water and gives off the silver effect.
Check out the 360 degrees video of Italy’s Glowing Blue Grotto!