Taking a deep dive in Helsinki’s subterranean city

A subterranean swimming hall beneath Helsinki’s granite bedrock, Itäkeskus uimahalli, opened in 1993 and now draws about 400,000 visitors annually, blending leisure with the city’s broader underground network. The facility, part of a master‑planned underground city approved in 2010, sits among a web of tunnels up to 90 metres deep that house shopping malls, playgrounds, a go‑karting track and subway stations, all designed to double as bomb shelters capable of protecting up to 900,000 Finns in wartime. The hall’s striking interior—white‑washed walls, a vast pool lined in vivid tiles, and a ceiling of suspended plastic triangles—offers a surreal swimming experience beneath an artificial moon, while entry includes access to a gym, hot tub, steam room and two saunas for a modest €6 adult fee.

The underground city concept emerged as Helsinki sought a more efficient solution for housing heating plants, telecommunications cables and other infrastructure without sacrificing surface land or green spaces. Rather than scattering utilities across expensive parcels and repeatedly excavating streets, the city repurposed bomb shelters originally carved during World War II, integrating them into a cohesive subterranean system. By 2010 the city council formally approved the world’s first officially master‑planned underground district, linking hundreds of human‑made caves and tunnels that serve everyday civic functions in peace and can be rapidly converted into protective shelters during conflict. This dual‑purpose design reflects Helsinki’s response to growing urbanisation and the need for resilient, space‑saving infrastructure.

Beyond the pool, Helsinki’s underground realm includes cultural venues such as the Amos Rex art museum and the rock‑cut Temppeliaukio church, both accessible via the same network of tunnels and also built to serve as shelters. Visitors experience a city that seamlessly merges everyday life with emergency preparedness, illustrating a model of urban planning that balances utility, recreation and safety. The author’s research, part of a three‑year study for the book *How to Build a City*, highlights Helsinki as a rare example of a city that has transformed its subterranean spaces into vibrant public realms while retaining the capacity to protect its population, offering a blueprint for other metropolises confronting uncertain futures.

⚡ Effects Interpreter