Finland carved an entire underground city into the bedrock beneath Helsinki, filling it with swimming pools, sports halls, parking areas, and shopping spaces that can be rapidly converted into blast-resistant shelters in case of war

Beneath the streets of Finland's capital lies a vast network of tunnels and facilities carved into solid granite. Hidden below Helsinki is a vast network of underground tunnels, sports centres, swimming pools, parking facilities and utility spaces that serve everyday purposes during peacetime but can rapidly transform into blast-resistant civil defence shelters if war or another major emergency strikes.

Raccontata datimesofindia.indiatimes.com