Ustica Green Cave is located in the southern part of the island, within zone C of the Ustica Island Protected Marine Area, and is part of a vast complex excavated by the sea when the altitude was different and the coast of noon it was higher up. The original cavernone is now divided into two parts, the upper part is called Sireta Cave, the lower part is called Green Cave or in the old Usticese dialect “A Rutta Vascia” (the lower cave). The prickly pears from the Mezzogiorno trail go up to its summit, the place is called “U Malu Passu“. The Green Cave has a very elongated entrance of about ten meters and with a height above the water of about 1.5 meters blocked by large rocks that emerge from a depth of about 7 meters that rises quickly towards the sea. ‘internal. It can be accessed with a small boat when the sea is calm, or by swimming. The internal environment is not vast, from the entrance to the bottom of the cave about 25 meters and a height of 15 meters. The surface is mainly occupied by large collapsed blocks that emerge from the water, a small stretch of free sea. The side walls of the cave, plunging into the water, widen and hence the origin of the famous and appreciated emerald green reflections.