In the Tyrrhenian Sea, off the Circeo, the Pontine Islands are a natural heritage of extraordinary beauty and have always enchanted anyone visited them. Ponza, the biggest island of the archipelago, is considered one of the most beautiful lands of the world by all naturalists, so that it deserves to be called "Pearl of the Mediterranean". In a few kilometres (7 km in length, 7 square km in surface, 41 km of coasts), Ponza gathers those numberless wonders which make it unique. Norman Douglas, the English writer dazzled by the Pontine Islands which he visited in 1908, wrote: "Only the adjective incredible would be appropriate to express the feelings aroused by those wide open caves on the sea, suffused with light as naves of cathedrals, or by those cliffs of lava or other minerals glittering of white, blood red, green, and pearl grey shades"