Photo via Mark Zuckerberg (CC-BY)
You probably never give much thought to where Facebook stores all your precious data. It's easy to imagine it just floating out there in the ether, but it's actually housed in massive data centers all over the world. In a post on the social network, CEO Mark Zuckerberg showed off one such facility, and it's more cold and efficient than you can possibly imagine.Hidden in the forests of northern Sweden, this particular data center employs roughly 150 people. As Zuckerberg notes, there are rarely any Facebook employees actually roaming the halls, because the design is so efficient that they only need a single technician to keep an eye on as many as 25,000 servers at once. Its location is crucial: The server room is cooled via ambient temperature. But when it's too cold outside, they switch the fans into reverse, and the heat of the servers is used to help warm the building itself. From the outside, you'd never know that countless selfies, memes, and political arguments are flowing through this building every single second of the day.