Soaring data-crunching demands, coupled with energy shortfalls, have motivated companies worldwide to invest in new, green, state-of-the-art data centres.

Some organisations have limited their green practices to the inside of newly constructed facilities, embracing modular grow-with-demand designs, energy-efficient IT hardware, virtualisation, DC power, and smarter cooling technologies. Others, however, have taken eco-friendliness a step further by transforming pre-existing structures into data centres.

Today, we'll take a look at some of the more innovative and unusual facilities that companies have selected to house their datacenters.

It's the bomb

Thirty meters below central Stockholm, housed in a former nuclear bunker, resides a 1,100-square-meter state-of-the-art data centre. Owned by Bahnhof, one of Sweden's largest ISPs, the facility - dubbed Pionen White Mountains, a throwback to its military origins - more resembles the lair of a criminal mastermind from a James Bond flick than it does a data centre.

It also offers a level of physical security you won't find at most data centres: 16-inch-thick steel vault doors separate it from the rest of the world - and it can reportedly withstand a hydrogen bomb blast.

Pionen serves as the home of the NOC for all of Bahnof's operations and as a collocation hosting center. Among its specs is 1.5 megawatts of cooling for servers, courtesy of Baltimore Aircoil fans (enough to chill several hundred rack-mounted machines); triple network redundancy with both fiber optics and extra copper lines; and two German Maybach MTU diesel submarine engines providing backup power.

These aren't repurposed engines, mind you; they just happen to be the same model you'd find in the aforementioned submarine. For laughs, the company also installed submarine sound horns to serve as the facility's warning system.

In the interest of making the facility an enjoyable place to work, the designers including niceties such as simulated daylight, greenhouses, waterfalls -- and a 2,600-litre salt water fish tank.