The biggest and most impressive crater on the island of Nisyros is called Stefanos, and is the center of attention for most tourists as it is one of the biggest and best preserved hydrothermal volcanoes in the world. The crater is ellipsoidal in shape its longest axe being 330 meters in length while its shortest is 260 meters. Its walls culminate at 30 meters while it is estimated to be 3.000 to 4.000 years old.