Helsinki turns abandoned oil caverns into giant underground heat battery
https://timesofindia.indiatimes.com/world/rest-of-world/helsinki-turned-abandoned-1970s-oil-caverns-into-a-giant-underground-heat-battery-holding-260000-cubic-metres-of-hot-water-it-can-heat-25000-homes-for-a-year/articleshow/133420847.cms
