The highly elongated island of Simushir (Остров Симушир) is the largest island of the Central group with an area of 353 km². The island is orientated northeast to southwest, measuring 58 km in length with an average width of around 6 km. The island of Ketoy lies 19 km to the northeast across the Diana Strait, and Chirpoy 67 km to southwest across the Boussole Strait. Simushir is constructed from a chain of extinct volcanic edifices: Urataman, in the northwest, forms a 7.5 km wide partially submerged caldera at the northwestern tip of the island (see large size Broutona Bay image); in the central region of Simushir lies the Zavaritzki Caldera (shown above), consisting of three concentric calderas of 10, 8 and 3 km across; also in the centre stands the 1,360 m tall symmetrical cone of Prevo Peak; the southwestern end of the island consists of the lobate peninsula formed by Mt. Milna — the islands highest point at 1,539 m.