Helsinki has built an extensive network of underground bomb shelters carved into the bedrock beneath the city, designed to protect the population in the event of a nuclear or other military attack, amid heightened concern in Finland over Russian aggression following the invasion of Ukraine. The shelters, part of Finland's long-standing civil defence policy, highlight how seriously Nordic countries bordering Russia are preparing for potential conflict, in contrast to less developed civil defence infrastructure elsewhere in Europe.

The underground network is reported to have capacity for around a million people, effectively covering Helsinki's entire population, with facilities including car parks, swimming pools and sports halls that can be rapidly converted into shelter space during a crisis. Finland, which shares a long border with Russia and joined NATO in 2023, has maintained mandatory shelter requirements in new buildings for decades, giving it one of the most developed civil defence systems in the world.