Blue Grotto (Capri), Italy

The Blue Grotto is a sea cave on the coast of the island of Capri Southern Italy. Sunlight passing through an underwater cavity and shining through the seawater, creates a blue reflection that illuminates the cavern. The cave extends some 50 meters into the cliff at the surface, and is about 150 meters deep, with a sandy bottom.

The cave is 60 meters long and 25 meters wide. The cave mouth is two meters wide and roughly one meter high. For this reason, entrance into the Grotto can only be achieved when tides are low and the sea is calm. Without calm seas and low tides, the Grotto becomes inaccessible, as the 1-meter entrance is impossible to pass. To enter the grotto, visitors must lay flat on the bottom of a small 4 person rowboat. The oarsman then uses a metal chain attached , both for safety reasons and to preserve water clarity.

The Blue Grotto is one of the several sea caves, worldwide, that flooded with a brilliant blue or emerald light. The quality and nature of the color in each cave is determined by the particular lighting conditions in that particulars 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 entrance way. 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 entrance way, 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, the primary source of light.

At the back of the main cave of the Blue Grotto, three connecting passageways lead to the Sala Dei Nomi, or Room of Names, named for the graffiti signatures left by visitors over the centuries. Two more passages lead deeper into the cliffs on the side of island. It was through that these passages were ancient stairways that lead to Emperor Tiberius palace. However, the passages are natural passages that narrow and then further along.