Kaliningrad, until 1946 known as Königsberg, is the largest city and administrative centre of Kaliningrad Oblast, a Russian exclave between Lithuania and Poland. The city sits about 663 kilometres (412 mi) west from mainland Russia. The city is situated on the Pregolya River, at the head of the Vistula Lagoon on the Baltic Sea, and is the only ice-free port of Russia on the Baltic Sea. Its population in 2020 was 489,359, with up to 800,000 residents in the urban agglomeration. Kaliningrad is the second-largest city in the Northwestern Federal District, after Saint Petersburg, the third-largest city in the Baltic region, and the seventh-largest city on the Baltic Sea.