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Inside Glesys Pori: a repurposed bedrock tunnel

2026-06-16

Underground facilities represent a small but growing niche in the global data center market, driven largely by the reuse of retired mines and Cold War-era bunkers across North America and Northern Europe. Stable temperatures, structural strength, and natural shielding give them advantages that new, purpose-built data centers struggle to match. One such facility, known as The Rock, sits in Pori on the west coast of Finland. Carved into solid bedrock, it spans 8,500 square meters of repurposed space, and today it houses IT infrastructure for companies across Europe.

From ammunition to potatoes, to data

The story of this place begins in 1965, when an explosion at a Finnish Defense Forces ammunition storage facility prompted the military to decommission similar sites across the country. One of those was a freshly carved tunnel complex just outside Pori, built but never actually used for its original purpose. Over the following decades, it served various roles, including, at one point, potato storage.

It took sixty years and a Finnish IT company called Ficolo to see what it could become. The tunnel structure, access routes, and utility supply were already in place. Converting the complex to data center standards took around six months. Today, the data center is the newest addition to the Glesys infrastructure portfolio: nine independent tunnel halls, 8,500 square meters of usable space, and a total site capacity of 11 MW.

“So far, three tunnels have been built and used as a data center, and six tunnels are still for expansion. So there’s definitely room to expand. Each hall is physically separate, so customers can run two completely redundant environments in the same facility”, says Jarkko Tuomisalo, Operations Manager, Pori data center.

“We have built airtight metal-clad structures inside the tunnels. That’s needed for fire suppression to work, and it lets us run the halls under slight overpressure to keep dust out. Inside, it behaves like any other data center, with the same airflow standards”, Tuomisalo continues.

Temperature and cooling

When you step inside, the temperature drops. Thanks to the surrounding bedrock, the facility sits at a stable eight degrees Celsius year-round. During harsh winters and summer heat waves, the baseline stays the same.

That consistency reduces the cooling load, but it does not eliminate the need for active cooling. In high-density deployments, heat accumulates regardless.

“Getting the heat out required drilling shafts straight up through 20 meters of rock to connect the cooling units inside to the equipment on top. In 2023, we also added direct liquid cooling to support denser workloads."

Renewable energy and built-in security

The data center runs on 100% renewable energy, with wind power forming the backbone of the supply and a 2,600-square-meter solar plant on the roof adding to it. Combined with the bedrock’s natural temperature stability, the cooling burden remains low, reflected in both their energy consumption and the environmental footprint of customers’ environments.
Security works the same way: the architecture does much of the heavy lifting before any modern system is added. The facility holds Katakri Level IV certification — the Finnish national security standard for handling classified information — and builds on that with biometric access controls (including access cards, PINs, fingerprints, and retinal scans), multiple security zones, and full CCTV coverage.

A different kind of data center

Not every workload needs to sit in a hyperscale campus on the outskirts of a capital city. Pori data center offers unique features that are difficult to find in a conventional above-ground build. And while it was not designed with data centers in mind, the Finnish Defense Forces built something remarkably well-suited for the job.

Jacob Andersson
About the author
Jacob Andersson is an inbound marketer at Glesys, focused on developments in cloud, infrastructure, and data center services.

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Inside Glesys Pori: a repurposed bedrock tunnel
2026-06-16
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Inside Glesys Pori: a repurposed bedrock tunnel
2026-06-16
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Inside Glesys Pori: a repurposed bedrock tunnel
2026-06-16
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