Today I learned that

Helsinki alone has more than 5,500 bunkers, with space for 900,000 people. Finland as a whole has shelter spaces for 4.4 million, in more than 54,000 separate locations. Most of these are private. By law, any building more than 1,200 sq m must make provision for a shelter. In addition to these are 44 large public shelters, built and maintained by the government. 

From The Telegraph, Inside the nuclear bunkers that will protect Finland’s citizens from war