||The site includes the far eastern part of the island Astypalaia and a complex of 14 islets, Kounoupi (140 ha), Fteno (2 ha), Chondropoulo (1.5 ha), Koutsomytis (40 ha), Moni (3 ha), Agia Kyriaki (23 ha), Tigani (4 ha), Chondri (30 ha), Ligno (18 ha), Fokionisia (60 ha), Katsagreli, Pontikoussa (90 ha), Ofidoussa (65 ha), and Ktenia. The island of Astypalaia belongs to the unit of Tripolis. The substratum of the site consists of Cretaceous limenstone in its major part. The north portion of the site consists of marine Pliocene sediments. All these islets, except Ophidousa, are surrounded by the depth curve of 100 m and consist of Cretaceous limentone. Ophidousa, lying 3 km west of Astypalaia, is joined with the main island with the depth curve of 200 m.The axis of the site has a NE-SW direction with a maximum length of about 11 Km and a maximum width of 9 Km. The islets Pontikousa and Ophidousa are characterized by a central hill, reaching at an altitude of 250 m and 130 m, respectively, high for their small surface, with very steep slopes. The vegetation is mainly phryganic but also includes Juniperus phoenicea arborescent matorral. At places, where the matorral is grazed and degraded, Pistacia shrubs have been appeared tending to dominate the vegetation. There are also intermittent streams with characteristic vegetation.The coastline is indended, with numerous small bays and typical sea-cliff vegetation. All along the coasline there are a lot of sea caves that are used as refuges by the Monk Seal Monachus monachus.