The Tool Desk
Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →Underground data centers are operating today, and interest in reusing mines and bunkers is growing. But they remain a small, specialized part of the data-center market—not a wholesale move away from conventional campuses. Their appeal is real: a strong existing structure, potential cooling advantages and a compact surface footprint. Whether those benefits outweigh difficult site access, water management, power and connectivity depends on the specific location.
What “having a moment” means
Industry reporting describes underground facilities as a small but growing niche, with examples in North America and Northern Europe. Operators have adapted former mines and hardened bunkers for data-center use. That is evidence of sustained interest, not proof of a sudden migration by hyperscalers or a replacement for conventional campuses. Uptime Intelligence analyst Max Smolaks told Data Center Knowledge in May 2026: “There are not many of them, but generally they seem to be working quite well.”
Different kinds of underground sites
The category includes distinct structures and operating models. Iron Mountain’s Boyers, Pennsylvania campus occupies a former limestone mine; Bahnhof’s Pionen facility is in a former civil-defense bunker beneath Stockholm. These examples show that underground data centers are not one standardized design: a mine and a bunker bring different structural, access and environmental conditions.
Lefdal offers a current scale marker
In a release dated March 11, 2026, investor 3i Infrastructure reported that Norway’s Lefdal Mine Datacenter had 37 MW operational and another 43 MW contracted and under construction. The company described six mine levels, with only one then used for data-center capacity, and a closed-loop seawater cooling system. Those are dated figures from an investor announcement, not live operating telemetry or a universal benchmark for underground facilities. 3i Infrastructure’s announcement also presents Norwegian power supply and the cooling approach as advantages of the site.
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Why build a data center underground?
Use an existing protective shell
Rock, mine infrastructure and bunker construction can provide a robust physical envelope and some protection from severe weather or external threats. The level of protection depends on the structure, its condition and how it is converted; “underground” does not mean invulnerable. Reusing an existing shell may also reduce surface-land needs, but conversion still calls for structural assessment, engineering, safety review and environmental scrutiny.
Make use of local conditions for cooling
Subsurface temperatures and nearby water may support particular cooling strategies. Lefdal’s closed-loop seawater system illustrates how a site can take advantage of local conditions, but it should not be treated as a standard feature of underground facilities. Operators still need a cooling design suited to the site and its computing loads.
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Match the site to the workload
A remote location may suit some high-performance computing or archival workloads if power, network routes and customer requirements align. It may be a poorer fit for services that depend on low latency or close proximity to users. These are site-selection considerations, not rules that apply to every workload or underground facility.
Iron Mountain design and construction executive Doug Titzer described the appeal to Data Center Knowledge in May 2026 as “a foundation of resilience, security, and inherent efficiency.” That is an operator’s characterization, not an independently established performance measurement.
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What makes underground construction difficult?
Retrofitting a retired mine or bunker for modern computing loads is not automatically cheaper or more efficient than building above ground. Before a project can rely on the existing structure, its condition, geology and ability to support the planned equipment and infrastructure need to be assessed. Older or unsuitable structures may require significant remediation or may not be viable.
- Water and humidity: Water ingress, damp conditions and humidity require careful management in below-ground spaces.
- Ventilation and cooling: The facility needs adequate air handling and a cooling system designed for its heat load and physical layout.
- Power and connectivity: A strong structure cannot compensate for inadequate, unreliable power or limited fiber routes. Capacity, redundancy, customer proximity and latency all matter.
- Delivery and maintenance access: Constrained routes can complicate moving heavy equipment in and out, as well as reaching the site for routine work or repairs.
- Expansion and approvals: Adding capacity may be less flexible than on a greenfield site, and conversion can involve safety, permitting and environmental constraints.
These are potential engineering and operating challenges, not a verdict on every mine or bunker. A site comparison needs to weigh them against the actual structure, infrastructure and intended use. The factors identified in Data Center Knowledge’s coverage and 3i Infrastructure’s Lefdal announcement include geology and structural condition, water risk, cooling design, power capacity and redundancy, fiber routes, expansion options, and equipment and staff access.
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Underground data centers are not the same as underground thermal storage
An underground data center has its IT equipment and facility space below ground. Cold underground thermal energy storage (cold UTES) instead stores cooling potential underground—in reservoirs or boreholes—for later use. A data center can use thermal storage without being physically underground.
In an August 11, 2026 report, the National Laboratory of the Rockies described a study with Lawrence Berkeley National Laboratory, the University of Chicago, Princeton and industrial advisers. It modeled cold UTES at 12 data centers in Arizona and Virginia. In one Virginia scenario, the model estimated 70% lower annual cooling-electricity costs—about $20 million per year for a 1-GW site. Separate model scenarios estimated $90 million to $390 million in reduced grid-infrastructure and fuel costs for a 1-GW reference hyperscaler. These are scenario outputs, not savings observed at a commercial deployment; the report says the work is moving toward commercial-scale demonstration sites. The laboratory’s study report also cites an EPRI figure that cooling can account for as much as 40% of annual energy consumption in computing facilities; the report does not state the year of the underlying EPRI publication.
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How to assess an underground data-center proposal
For a construction or infrastructure decision, evaluate the site as a whole rather than assuming the underground location is itself an advantage:
- Establish structural and geological suitability. Review the condition of the mine or bunker, its stability, and the risks associated with water and the surrounding geology.
- Test the cooling plan against the actual site. Identify the proposed cooling method and determine whether its energy-performance claims are independently substantiated for comparable operating conditions.
- Verify power and network capacity. Check available power, redundancy and fiber routes against the intended load, customer locations and latency needs.
- Plan for the full operating life. Assess equipment delivery, staff access, maintenance, ventilation, water management, permitting and environmental constraints, as well as how the site could expand.
The case for going underground is strongest when the structure, utilities, cooling opportunity and workload align. If critical infrastructure or access is weak, the protective shell alone cannot make the site a sound choice.
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