Helsinki, Finland CNN  — 

On the busy streets of Finland’s capital, Helsinki, security preparations are underway to host a much-anticipated summit between US President Donald Trump and Russian leader Vladimir Putin.

But deep beneath the streets, hewn into the granite, lies a vast network of tunnels and caverns that provide this Nordic nation with its last line of civilian defense.

Helsinki's network of tunnels can fit the city's entire population.

In the event of a military attack, officials in Helsinki say the entire population of 640,000 could be sheltered in the solid rock bunkers, equipped with food, bedding, sanitation, hospitals – and even an underground ice hockey rink.

“We are taking care of the whole population of this country,” said Karim Peltonen of the Finnish National Rescue Association, which manages the tunnels.

“When we are defending the country we also have to have the appropriate civil defense capability.”

A subterranean ice hockey rink in Helsinki.

Finland struggled for more than a century to assert its independence from the Kremlin.

With its long Russian border and painful history of Russian invasion, Finland has strived to balance the interests of its giant neighbor and its own independence.

This means not opposing Russia, but also not being allied to it, a delicate stance known as “Finlandization.” The term also captures how Finland, now a member of the European Union, remained officially neutral during the Cold War. It’s a status that has involved compromises.

There are no illusions here about what the biggest threat to Finland is.

“It’s Russia that’s a potential enemy,” Peltonen said as he showed CNN around a nuclear bunker, 18 meters below ground.

Finland’s historical neutrality and its proximity to Russia made it a choice venue for Cold War era summits, characteristics that have once again thrust it into the spotlight.

It’s not clear what Trump and Putin will agree here in Helsinki on Monday, and few details of their meeting inside the tightly guarded presidential palace have been revealed.

The Presidential Palace in Helsinki, where Trump and Putin will meet on Monday.