Usedom is a Baltic Sea island in Pomerania, since 1945 split between Germany and Poland. It is the second biggest Pomeranian island after Rügen and before neighbouring Wolin. It is situated north of the Stettin Lagoon estuary of the River Oder. About 80% of the island belongs to the German district of Vorpommern-Greifswald in the state of Mecklenburg-Vorpommern. The eastern part and the largest city on the island, Świnoujście (German: Swinemünde), are part of the Polish West Pomeranian Voivodeship. The island's total area is 445km2 (the German part 373km2; the Polish part 72km2). Its population is 76,500 (the German part 31,500; the Polish part 45,000). With an annual average of 1906 sunshine hours, Usedom is the sunniest region of both Germany and Poland, and it is also the sunniest island in the Baltic Sea. Hence its nickname Sunny Island . The island is a very popular tourist destination since the Gründerzeit in the 19th century, and features unique heritage of this era, like its many noble mansions in resort architecture. Notable seaside resorts include Zinnowitz and the Amber Spas in the west, the Kaiserbad and Świnoujście in the east.