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Beneath this Orthodox Christian cathedral in Helsinki is a datacentre designed to pipe heat to nearby homes.
The datacentre is located in a former WWII bunker carved into the rock below Uspenski Cathedral.
Heat from the hundreds of computer servers in the datacentre is captured and transferred to water-filled pipes and then used to heat homes in the Finnish capital.
The amount of heat transferred should be enough to heat about 500 homes.
The energy usage of the datacentre, used by IT services firm Academica, is designed to be half that of a typical datacentre.