In a civil defense shelter hewn into rock, behind doors designed to withstand a nuclear or biological attack, two Finnish conscripts wearing hazmat suits and breathing masks are measuring radiation levels as they take part in an exercise to turn a cave into a place of safety for thousands of people.

Inside, in what is normally a sports hall, hundreds of people are sleeping overnight on trestle beds.

More than 2,000 people including volunteers and students are taking part in the biggest civil defense exercise in Europe since the end of World War II. In the scenario, critical infrastructure in the central Finnish city of Kuopio, including power and water, has been disrupted by cyberattacks and there's the threat of missile strikes from Finland's neighbor, Russia.