1. Pionen data centre, Sweden
Located in a Cold War era defence bunker, this data centre could take a hit from an H-bomb and keep on ticking. It takes advantage of some other military technology, enlisting dual submarine engines to power backup generators in case the conventional power grid fails. To make the working day bearable in a granite cave 100 feet below the streets of Stockholm, the facility has greenhouses, an artificial waterfall and a 686-gallon salt water fish tank.