Facebook CEO Mark Zuckerberg started sharing some rare photos of its data center in the forests of Northern Sweden, where Facebook is taking advantage of the low temperature and nearby rivers to increase efficiency and save power. The massive Luleå data center, which is the size of six football fields, uses enormous fans to “pull in the outside air to naturally cool the thousands of warm servers that line the center’s broad hallways,” writes Zuckerberg in a post on his Facebook page. He adds: