• There are 5,500 bunkers in Helsinki, creating a vast network of underground facilities that have been built since the 1980s.
• And although they're usually used for parking, storage, sporting events and more, their true purpose is more ominous: they are designed to protect those in Finland from attack.
• Finnish authorities do not think there is an imminent threat to the country, but having been invaded by the former Soviet Union in the past and witnessing the recent war in Ukraine, the Nordic nation wants to be prepared for the worst.

HELSINKI, Finland — Blast proof, gas proof and offering protection from radiation and toxic chemicals — Finland takes its network of underground bunkers seriously.

Located about 60 feet underground, this civil shelter in Helsinki can hold up to 6,000 people. Defying expectations of a dark, damp cave; it's bright, clean and warm, complete with soccer pitch, children's playground, cafeteria and car park.

There are 5,500 similar bunkers across the city, creating a vast network of underground facilities that have been built since the 1980s.

And although they're usually used for parking, storage, sporting events and more; their true purpose is more ominous: they are designed to protect those in Finland from an attack.

Speaking to CNBC from inside a bunker, Tomi Rask, a preparedness teacher at Helsinki City Rescue Department, said that all types of weapons had been taken into account when designing the shelters.

"Blast proofing, gas proofing, radiation and toxic chemicals," he said.

These bunkers also have to be able to be converted and ready for use as defense shelters within 72 hours.

"We need to make room for people that are coming into the shelters and that means that some structures, some objects need to be taken away," he added.

"But it's not that we need to [fully] empty the shelter before we can take persons in because in sheltering time, you'll need to have some form of equipment," he added, explaining that a car, for example, can provide some private space to a family.

The playground is also considered important during sheltering time, to enable children to let off steam and parents to have a break.

These civil shelters "might be the one thing that we could give to NATO," Rask added.

NATO membership

His comments come as Finland prepares to apply to join the 30-member military alliance, despite decades of military neutrality.

On Sunday, Finland's President Sauli Niinisto said being a member of NATO will "maximize" Finland's security after Russia's unprovoked invasion of Ukraine in February.

Russia's invasion of Ukraine had changed Finland's security situation, according to Niinisto, although he does not believe there is an imminent threat against the country.

However, as Finland shares an 830-mile border with Russia and has been invaded by the former Soviet Union in the past, the Nordic nation wants to be prepared for the worst.

"We have neighbors. And naturally the neighbors might cause us some immediate danger," Rask said about the reasoning behind these bunkers.