Kassari is the fifth biggest island in Estonia, its area is 19.3 square km. Its coast is washed by the waters of Jausa, Käina, Vaemla, Kassari and Õunaku bays.
Kassari rose from the sea 3000 years ago and the highest point on the island is 15 meters above the sea level. There is a 3 km long pebbly peninsula Sääretirp in South-Western part of Kassari.
Nearby is sandy Piibunina seaside, which is a good place for swimming thanks to its rapidly warming waters.