"My! Have we got to squeeze under there!" exclaimed Peachy wonderingly, looking at the tiny space at the foot of the crag through which they would be obliged to pass. "Not in these boats, of course," said Vincent. "The skiffs are waiting, and if we just leave it to the boatmen they'll show us how to manage." The tiny craft that were in readiness for visitors now came forward, and the party was transferred to them. Three passengers were taken in each skiff, and were required to lie flat on their backs in the bottom of the boat. The boatman paddled to the entrance of the grotto, then also lying on his back he directed the skiff into a low passage, working his way along by pulling at a chain which was fastened to the roof of the rocky corridor. In a short space of time they shot into an enormous cavern, 175 feet in length, and over 40 feet in height. Here for a moment or two all seemed dazzled, but as their bewildered vision gradually grew accustomed to the light they saw that everything in the grotto, walls, sea, or any objects, appeared of a heavenly blue color. The faces of their friends, their own hands, the water when they scooped it up and dropped it again, all were turned to sapphire, while articles under the sea gleamed with a beautiful silver shade. The girls bared their arms and enjoyed dipping them to obtain this effect. The glorious blue of the cave was indescribable. "I feel like a mermaid at the bottom of the ocean," exulted Peachy. "Or a cherub in the sky!" said Jess. "Why is it blue though?" asked Lorna. "Because of the refraction of light," explained Mrs. Beverley from the next boat. "We see a kind of concentrated reflection of the sky sent to us under the sea. If it were a gray day outside it would be gray in here too. Some people think that the Mediterranean has risen, and that once the water in this grotto was much lower, so that boats could sail in and out of it quite easily. Do you see that landing-place over there? It leads to some broken steps and a blocked-up passage that tradition says wound up through the cliff right to the villa of Tiberius. Perhaps it was a secret way by which he thought he might escape if danger threatened him." "How I'd love to explore it," sighed Irene. "It only goes a little way before it is blocked. It's hardly worth landing to look at it. Be careful, Renie! If you lean over the edge of the boat so far you'll be upsetting us, and, although we might look very delightful and silvery objects under the water, I'm not at all anxious to offer myself for the experiment." "Why don't they enlarge the entrance?" asked Vincent.