The Secret Beneath Helsinki: Exploring Finland's Incredible Underground City

The Secret Beneath Helsinki: Exploring Finland's Incredible Underground City

HELSINKI, Finland

Beneath the streets of Helsinki lies one of the world's most sophisticated underground urban networks. However, it's not a single hidden "city" with streets and homes. Instead, it is a carefully planned network of tunnels, underground facilities, technical infrastructure, sports complexes, parking areas, utility systems, and civil defence shelters built into solid granite bedrock. It is often referred to as Helsinki's Underground City or the Underground Master Plan.

What exactly is the Underground City?

Unlike fictional underground cities, Helsinki's underground world serves practical everyday purposes while remaining ready for emergencies.

It includes:

1. Underground roads and tunnels
2. Metro stations
3. Shopping connections
4. Car parks
5. Sports halls
6. Swimming pools
7. Ice rinks
8. Energy plants
9. Water supply systems
10. Data and utility tunnels
11. Civil defence shelters

During peacetime, these spaces function normally. In an emergency, many can be converted into bomb shelters within about 72 hours.

When did it begin?

Helsinki has been building underground facilities for decades.

Timeline

1. 1960s–1980s
2. Construction of major underground tunnels and infrastructure began.
3. 1980s
4. Helsinki started maintaining an underground space allocation plan.
5. Early 2000s
6. The city decided to prepare a comprehensive Underground Master Plan.
7. 2004
8. Planning principles officially approved.
9. 2010
10. Helsinki City Council approved the Underground Master Plan, making Helsinki one of the first cities in the world with a legally adopted underground master plan.

Why was it built?

Finland's history largely explains the decision.

During:

1. Winter War (1939–1940)
2. Continuation War (1941–1944)

Finnish cities experienced heavy bombing. Since then, Finland has invested heavily in civil preparedness.

Another reason is geology. Helsinki sits on extremely hard granite bedrock, making it ideal for carving durable underground spaces.

How large is it?

Although there is no single underground "city," the underground network is enormous.

Current estimates include:

1. More than 400 underground facilities
2. Over 200 km of tunnels
3. Hundreds of reserved underground sites for future development

The Underground Master Plan continues to expand as Helsinki grows.

Bomb shelters that become sports centers

One of Helsinki's most famous features is its dual-use design.

For example, the Merihaka Civil Defence Shelter normally operates as:

1. Sports halls
2. Gym
3. Children's playground
4. Recreation facilities

If needed, it can be transformed into a shelter for approximately 6,000 people within 72 hours. Reuters reported in 2026 that this facility has become an international model, attracting hundreds of foreign delegations interested in Finland's civil defence approach.

Can the shelters protect everyone?

Finland has one of the highest levels of civil defence preparedness in the world.

Nationally:

1. Tens of thousands of civil shelters exist.
2. Shelter construction is mandatory for many larger new buildings.
3. The country has shelter capacity for most of its population, with Helsinki itself having exceptionally extensive coverage through both public and building-specific shelters.

What can visitors actually see?

Many underground places are open to the public.

Examples include:

1. Metro stations
2. Underground shopping connections
3. Underground parking facilities
4. Rock-carved swimming halls
5. Sports complexes

Most technical tunnels and civil defence infrastructure are not open to the public for security reasons.

Why is the world paying attention now?

Russia's invasion of Ukraine renewed international interest in civil preparedness.

According to Reuters (2026):

1. Officials from Ukraine
2. Poland
3. Germany
4. Middle Eastern countries

have visited Helsinki to study its underground infrastructure.

Finnish companies specializing in shelters are also seeing growing international demand.

Interesting facts

1. The underground spaces stay at a relatively stable temperature year-round.
2. Granite provides excellent protection and structural stability.
3. Many spaces have independent ventilation, water, electricity, and emergency systems.
4. Some metro stations are also designed to function as shelters in emergencies.

Present situation (2026)

Today, Helsinki continues to expand and manage its underground infrastructure through long-term urban planning. The city's 2025 implementation programme explicitly continues to use the Underground Master Plan alongside the main city plan to guide future development. The network is considered a key part of Helsinki's resilience, supporting everyday city life while remaining ready for emergencies.

Sources

1. https://www.hel.fi/en/urban-environment-and-traffic/urban-planning-and-construction/planning-and-building-goals/city-plan
2. https://www.hel.fi/static/liitteet/kaupunkiymparisto/julkaisut/julkaisut/julkaisu-11-18.pdf
3. https://www.reuters.com/world/europe/finlands-massive-bomb-shelters-draw-world-helsinki-quest-security-2026-05-21/

This is one of the reasons Helsinki is frequently cited by urban planners and civil defence experts as a global leader in integrating underground infrastructure into everyday city life.