The Grotta del Sangue ( Blood Cave), so called for some red concrections in the sub aerial part . It's a typical marine origin cave, carved by waves in the lime stone rock: low depth, no cave formations, bottom slowly rising and presence of ripple marks (bottom ondulations of pebbles or sand , created by the waves. In fact where the cave stops (-3 mt) there Is a sand accumulation. Very clear is the warm sulphureous water spring with white sul­phur bacteria colonies. We see the thermic and saline stratification and slipping in a hand (without glove) we feel the difference in temperature. A lot of tourist boats visit the Grotta del Sangue, so stay dose to the bottom and don't surface. In one side the "variant" opens, a tortuous cuniculus for very experienced divers, leading to the inner lake where we admire an ancient shore levels stratification. During the safety stop before surfacing, good observers will see the young leaf snail Elysia timida.