Pionen

Pionen is a former civil defence center built in the White Mountains Södermalm borough of Stockholm, Sweden in 1943 to protect essential government functions.

It was converted into a data center by the Swedish Internet service provider Bahnhof.

[1][2] Because of the facility being buried under the mountain, secured by a 40-centimeter thick door, and only reachable by an entrance tunnel, the data center is capable of withstanding a hydrogen bomb.

[citation needed] Pionen is a data center deep below 30 meters of granite, with three physical datalinks into the mountain.

Pionen features fountains, greenhouses, simulated daylight and a huge salt water fish tank.

Pionen in 2006, before it became a data center.