As Russia’s war with Ukraine threatens to spill over into Europe, nations around the world are rapidly restoring and expanding their network of shelters to keep people safe in the event of a chemical, biological or even nuclear attack. Shelter construction companies have been heading to Finland and Switzerland to see what it takes to build a bunker that can withstand modern day threats. WSJ traveled to Finland to check out one of the country’s largest modern nuclear shelters that can keep 7,000