Modern cities are not only expanding upward – they are increasingly growing underground. The concept of the underground city is becoming a crucial part of urban development worldwide, helping cities tackle land scarcity, climate adaptation, and urban resilience in densely populated areas. Far beyond simple subway tunnels, today’s underground spaces function as complex, interconnected districts that redefine how cities use and shape their land. This article explores what makes a successful underground city, its opportunities and risks, and real-world examples that point the way forward.

Why Cities Are Digging Deeper

Urban densification creates intense competition for limited surface space. At the same time, climate resilience, flood protection, and the need for flexible infrastructure demand new solutions. An underground city allows transport systems, utilities, retail, and even leisure spaces to be separated from the busy street level, making room for more green spaces and improving quality of life above ground.

Security is another factor: underground shelters and protected facilities have long been part of national resilience strategies in countries such as Switzerland and Finland. In the context of climate change and geopolitical risks, the underground city can even serve as a lifeline during emergencies.

A Look Back: The Roots of the Underground City

Using underground space is not a new idea. From ancient catacombs to vast metro systems, cities have long looked below the surface to meet practical needs.

A leading example of a functional underground city is Montreal’s “RESO”, a 32-kilometer network connecting shopping malls, metro stations, offices, and residences. In winter temperatures as low as -30°C, this underground city ensures that daily life can continue comfortably and safely – a powerful demonstration of how urban life can be decoupled from harsh surface conditions.

Underground Cities as Climate-Resilient Districts

Today, more cities are rethinking their below-ground potential. Helsinki has become a global pioneer of the underground city approach. For decades, the Finnish capital has followed an official Underground Master Plan that governs what can be built underground and where. This ensures safe, conflict-free use of the city’s bedrock. Helsinki’s underground city includes public swimming pools, ice halls, parking garages, utility networks, and even data centers — all tucked away beneath the urban fabric.

Singapore is another city-state pushing the limits. Its “Underground Master Plan” aims to systematically move industrial and utility functions underground, freeing up the surface for parks, housing, and biodiversity. In this way, the underground city model helps solve land scarcity while advancing climate adaptation goals.

Architectural and Technical Innovations for Underground Cities

Designing an underground city comes with unique architectural and engineering challenges. Ventilation, lighting, and wayfinding must create spaces that feel safe and pleasant to use. Modern solutions include daylight-guiding systems, LED light panels, and carefully designed access points that connect underground and surface seamlessly.

Projects like Osaka’s Namba Parks, with its terraced green roofs and courtyards, bring natural light deep underground. The Dutch architecture firm Mecanoo has applied similar principles to underground libraries in Delft and Kaohsiung, proving that the underground city can be welcoming and inspiring.

An underground city can also deliver energy efficiency. Norway’s Lefdal Mine Datacenter is housed in a former mine and uses cold fjord water for natural cooling – a prime example of how underground facilities can reduce carbon emissions while supporting the digital economy.

Potential Risks: Safety and Social Inclusion in the Underground City

Despite its many benefits, an underground city poses risks. Poorly designed underground spaces can become isolated, unsafe, or socially segregated. In Beijing, thousands still live in former Cold War bunkers under precarious conditions – highlighting the need for strong regulation and inclusive design.

Safety standards, evacuation routes, and emergency power must be carefully planned. Architects stress that an underground city should feel intuitive, secure, and accessible – with clear signage, good acoustics, and natural light whenever possible.

Global Examples: What Cities Can Learn

• Helsinki: A comprehensive underground master plan avoids conflicts and ensures safe, efficient use of space.
• Montreal: The “Underground City” illustrates how climate resilience and urban comfort can go hand in hand.
• Singapore: Systematically relocating industry and utilities underground frees up the surface for urban green spaces.
• Beijing: China’s capital shows the other side: thousands still live in former Cold War bunkers, highlighting the risks of unregulated underground use.

Conclusion: The Underground City as a Key to Sustainable Urban Futures

An underground city is far more than hidden tunnels and pipes – it’s a strategic layer of modern urbanism. When designed with care, underground cities can tackle the biggest challenges of dense urban areas: limited land, climate adaptation, and urban resilience.

The lessons from Helsinki, Singapore, and Montreal show that invisible infrastructure can become a vital part of the livable city – if it’s not just hidden, but well-designed, accessible, and welcoming. The underground city will shape how future generations live, move, and connect –  both above and below ground.

Read more about climate change in cities here.