The underground city of Helsinki functions daily as a network of swimming pools, gyms, playgrounds, tracks, parking lots, cultural spaces, and even a church. Under the Finnish capital, nearly 500 facilities total 10 million cubic meters and can be converted into fully operational civil shelters within 72 hours during major urban emergencies.
The underground city beneath Helsinki comprises nearly 500 facilities carved into the bedrock of Finland’s capital. Approximately 10 million cubic meters are occupied by swimming pools, gyms, sports tracks, playgrounds, parking lots, metro stations, cultural spaces, rehearsal rooms, commercial areas, a museum, and even a church.
The numbers were presented in January 2026 by the institutional portal This is Finland, produced by the Finnish Ministry of Foreign Affairs, and complemented by a Reuters report published on May 21, 2026. The structures are used daily but must be fully available as civil shelters within 72 hours in case of an emergency.
Underground city operates every day
Most of the facilities do not remain closed waiting for a war or disaster. Residents use the spaces to swim, play sports, play with children, park vehicles, rehearse music, travel by metro, and cross commercial areas protected from external weather conditions.
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The underground city has been integrated into Helsinki’s routine so that the infrastructure does not become an empty and unknown space. Continuous use also facilitates maintenance and allows the population to recognize the locations before a potential emergency situation.
Nearly 500 facilities occupy the underground
Helsinki has approximately 10 million cubic meters of underground areas distributed across nearly 500 facilities. The scale has led the capital to develop a specific plan to organize the use of the underground and avoid conflicts between tunnels, services, transport, and new constructions.
The region’s granite base favors the excavation of large halls, passages, and sports complexes. The rock allows for the creation of spacious areas, with high ceilings and an appearance very different from the narrow and dark image usually associated with bunkers.
Network can protect nearly 1 million people
The Finnish capital has about 5,500 smaller shelters and 48 large collective protection structures. Together, the spaces offer a capacity close to 1 million people, a number higher than the population of approximately 700,000 residents of Helsinki.
This margin also considers workers, students, visitors, and people who may be in the city during an emergency. The planning is not limited to the number of officially registered residents but seeks to accommodate anyone in the urban area when the system is activated.
Spaces need to be ready in 72 hours
Everyday use facilities must be converted into fully operational civilian shelters within 72 hours. During this period, sports and commercial activities may be suspended for the installation of beds, water tanks, portable toilets, and other emergency equipment.
The requirement forces public and private managers to maintain access, ventilation, protective doors, electrical networks, and sanitary systems in suitable conditions. The rapid transformation depends on equipment already stored and plans defined before a crisis occurs.
Largest shelter accommodates 6,000 people
The Merihaka shelter is presented as the largest dual-use complex in the city and can accommodate approximately 6,000 people. The facility has 71,000 cubic meters, a volume comparable to that of a seven-story commercial building.
Built in 2003, the space is about 25 meters below ground and daily houses sports courts, a gym, and a children’s playground. In an emergency, the leisure environment can be reorganized to accommodate thousands of people without relying on the construction of a temporary structure.
Pool can become shelter for 3,800 people
The Itäkeskus aquatic complex was opened in 1993 and receives about 375,000 visitors per year. Built under approximately 50 meters of rock, the site includes pools, saunas, gyms, and areas designated for sports practice.
If necessary, the pools can be emptied and the complex converted into a shelter for about 3,800 people. The environment that normally hosts swimmers and families was designed to take on a completely different function in a few hours.
Playground is 30 meters below the streets
In the Hakaniemi district, the Play Cave operates approximately 30 meters below the surface. The space features trampolines, slides, ball pits, padded structures, and areas where young children can safely practice movements.
The daily presence of families changes the relationship of the population with the protective infrastructure. For a child, the potential shelter would not be an unfamiliar place, but the same environment where they have already played in normal situations.
Gym operates eight floors below ground
The Maunula Sports Hall is located in an area estimated to be about eight floors below the surface. The complex welcomes people who practice weightlifting, stretching, dancing, and table tennis during different periods of the week.
Users highlight the lighting, space, and air circulation within the facilities. Despite the depth, the environment was designed to function as a common sports facility and not as a structure permanently associated with fear.
Kart track was carved into the rock
In the Myllypuro district, an indoor kart track is approximately 300 meters long and was built deep into the bedrock. The underground operation maintains similar conditions throughout the year, regardless of rain, snow, or wind.
Like other dual-use spaces, the track is part of the city’s civil defense network. The Finnish logic transforms areas that could remain idle into facilities capable of generating economic activity, leisure, and permanent maintenance.
Churches, museums, and metro occupy the underground
The underground city includes metro stations, parking lots, pedestrian passages, commercial areas, rehearsal rooms, Olympic Stadium facilities, and cultural spaces. Among the well-known locations are the Temppeliaukio Church and the Amos Rex Museum.
Some metro stations have also been prepared to function as civil shelters. The underground system does not form a single continuous hall but a distributed network of facilities connected to the city’s daily operation.
Construction of shelters is mandatory by law
Finland has required for more than 70 years the construction of shelters in certain buildings. According to the Ministry of the Interior cited by Reuters, residential and commercial buildings with an area greater than 1,200 square meters must include this type of structure.
The building owner bears the costs, estimated between 1.5% and 4% of the total value of a new residential construction. The legal obligation has helped spread thousands of shelters throughout the country, rather than concentrating them only in large public facilities.
Finland has more than 50,000 shelters
The national network totals approximately 50,500 civil defense structures. Continuous construction began in 1955, influenced by the Finnish experience during World War II and the geographical proximity to Russia.
During the Cold War, planning mainly considered the possibility of a nuclear conflict. After the Chernobyl accident in 1986, the system also began to incorporate concerns related to radiological accidents and other technological risks.
Equipment protects against different threats
The shelters use resistant doors, special ventilation systems, emergency power supply, communication networks, and water and sewage structures. The maintenance of these components is necessary even while the spaces serve sports or commercial functions.
Finnish companies have specialized in the manufacture and care of these solutions. Protection depends less on the appearance of the walls and more on the technical ability to maintain air, water, energy, and communication during a prolonged emergency.
Foreigners seek the Finnish model
About 800 foreign delegations have already visited the Merihaka shelter to learn about the organization of dual-use spaces. Political representatives, administrators, and companies seek to understand how Helsinki combines daily activities with civil preparedness.
Interest has increased with the wars in Ukraine and Iran, according to Reuters. Authorities and companies from European and Middle Eastern countries have started to evaluate Finnish technologies related to protective doors, ventilation, communication, and emergency energy.
Ukraine wants to combine shelter and activities
Representatives from Ukrainian cities visited Helsinki with an interest in building sports complexes capable of also functioning as protection against attacks. In areas near the front, warning sirens can sound 15 times a day or more.
In the city of Balakliia, a shelter built over a year also functions as an underground school. The proposal is to allow children to continue studying protected from drones and missiles, instead of just waiting for the alerts to end.
Daily use keeps structures familiar
For the Helsinki Rescue Department, keeping the shelters in use facilitates conservation and reduces unfamiliarity in an emergency. People know the accesses, corridors, and characteristics of the locations before they need to stay in them out of necessity.
The strategy also makes it economically justifiable to excavate large spaces in granite. Pools, gyms, parking lots, and cultural areas help return to society part of the investment made in civil protection.
Second city continues to expand
A Helsinki underground network is not complete nor does it remain static. New facilities, renovations, and adaptations are incorporated as urban, technological, and safety needs change.
The result is an underground city that combines mobility, leisure, culture, and protection for almost 1 million people. Would you feel safer living in a city where pools, gyms, and playgrounds can transform into full shelters in up to 72 hours? Leave your opinion in the comments.
