There are numerous caves on the island of Bisevo, Croatia, but the Blue Grotto, which can only be reached by boat, is the most famous of them, due to the glowing blue light that appears from 10 am to noon. At this time of day the sunlight reflects through the water coming from the white floor of the cave and bathes the grotto in aquamarine light, while objects in the water appear to be silver.
Blue Magic on Biševo (Croatia). 'Of the numerous caves around the remote limestone island of Biševo, the Blue Grotto (Modra Špilja) is the most spectacular. On a clear morning, the sun’s rays penetrate through an underwater hole in this coastal cave, bathing the interior in a mesmerising silvery-blue light. Swimming inside is a surreal must-have experience – worth a trip to this far-out island. http://www.lonelyplanet.com/croatia
Zakynthos (Greece), also known by its Italian name Zante, battles against heavy package tourism along its eastern and southeast coasts. Underneath the brouhaha it is essentially a beautiful island with western and central regions of forested mountains dropping off to unreal turquoise waters... Read more: http://www.lonelyplanet.com/greece/zakynthos#ixzz3LKC8RIQI