What may be the most ambitious underground city ever constructed is currently taking shape below Helsinki, Finland. A series of subterranean complexes house stuff that would otherwise take up valuable space in the metropolitan communities above ground -- data centers, energy infrastructure, parking structures, and heating facilities. Not only does this leave room up top to more efficiently and pleasantly develop walkable city neighborhoods, but the cooler temperatures help save energy on the industrial operations:http://tumblr.com/x2p1qzbayv

"The world's greenest data center lies 30 meters below the ground surface of a cathedral in Helsinki, Finland," the Huffington Post reports. "The underground green data center cuts down on energy consumption by cooling their computers with sea water, and using the excess heat to warm Helsinki homes. Normally, nearly half of the energy used in data centers goes towards cooling down the computers."

According to CNN, Helsinki is the first city to attempt constructing a subterranean component to its city on such a large scale. As illustrated in the video, Helsinki is especially suited for the undertaking, thanks to the exceptionally strong bedrock on which the city sits.

It's a pretty fascinating project, and certainly a good way to maximize space and efficiency. Now we just have to do something about all that coal ...