It is convenient: a tunnel just a stone’s throw from the lecture halls.
Laboratory engineer Otto Hedström guides visitors below ground. A small statue of Saint Barbara stands at the entrance to the test tunnel, welcoming visitors. The saint protects those working with artillery and explosives, and in many European countries she’s an important symbol for tunnelling and mining.
Hedström’s job is to take care of the test tunnel. He assists researchers and research groups in their projects and teaches students hands-on skills such as rock drilling. The ‘classroom’ in a cavern niche consists of a long table, benches, and presentation equipment. The tunnel is filled with tools of all sizes.
‘We have everything needed for small-scale tunnel construction. The yellow pipes overhead are for ventilation. If we do something that produces a lot of smoke or dust, we’ve got a solid ventilation system,’ Hedström explains.
Accompanying us are students from the European Mining Course master’s programme. Understanding rock and underground conditions is essential in both mining engineering and rock construction.
A former mining engineer, Hedström says curiosity about what lies underground led him to the field. Tunnels and rock structures were a mystery he wanted to understand.
‘For me, it’s a fascinating combination of practical work inside the tunnel and collaboration with research groups – turning theoretical research questions into practice.’
Cubes attached to the rock wall bear markers that can be automatically recognised by computers. Here, researchers study imaging methods: LiDAR scanning, photogrammetry and the Gaussian splatting visualisation technique. Imaging allows analysis of rock mass stability, displacements, and weaknesses.
There is a key difference between construction above and below ground: on the surface you add material; underground you remove it. Assistant Professor Lauri Uotinen says the biggest challenge is that the rock is already under stress.
When material is removed – by open-pit excavation or tunnelling – the stress field changes. ‘You must ensure the rock remains stable and doesn’t collapse on you. Once you have the desired shape, you use shotcrete and rock bolts, and in some cases safety nets, to ensure the structure remains stable throughout its lifecycle.’ Bolts in the ceiling prevent large blocks from falling, while shotcrete on the walls prevents smaller fragments from coming loose.
In the test tunnel, cutting-edge research and traditional work coexist. Automation, digitalisation, and remote operations are now central to rock engineering and mining, and students are exposed to all of it. Reducing emissions is another major theme: Aalto researchers are developing recycled and biopolymer materials to replace shotcrete, for example.
But now, the students climb aboard an orange 1980s-era work machine – this time just for photos. The machine is still operational but is awaiting repair. It drills holes in rock to be filled with dynamite for blasting.
‘As you can see, the walls are full of holes. It’s getting hard to find a spot that hasn’t been drilled. In the future, we’ll extend the tunnel below this level,’ Hedström says.
Holes in one wall are marked in different colours. Hedström explains that this simulates real tunnel construction: small detonators create a controlled blast.
‘It makes a lot of noise and smoke, but the blast isn’t strong enough to fracture the rock. You can’t compare this to a PowerPoint in a classroom – once students have done this, they remember it.’
Building into rock is a multi-stage process requiring expertise from many fields. Uotinen says everything starts with geological investigations: geologists drill holes and inspect core samples or perform geophysical measurements on site. ‘This allows us to characterise the rock and determine the best location for the project and whether there are weak zones or water-bearing areas that must be considered.’
Rock-construction professionals design the spaces. Many underground projects now also include the work of architects, just like any above-ground construction.
‘From there, construction becomes very similar to what happens above ground: you have structural engineers and designers for electrical, HVAC and automation systems.’
Good lighting design is crucial underground, as there is no natural light. Fire safety and ventilation also require special attention. ‘If a fire starts in a rock cavern, the space fills with smoke quickly. You must plan pressurised escape shafts and routes so visibility is maintained and people can evacuate. Winter brings other problems: if sub-zero air is blown in, ice can start forming, so the air needs preheating.’
Being underground doesn’t feel pleasant for most people. Comfort can be improved through surface materials, lighting, and sound design. Large halls and tunnels often have abundant signage – far more than above ground.
‘After five minutes underground, you have no idea which direction you’re going. Wayfinding is essential,’ Uotinen says.
An orange metro train brakes into Tapiola station, and passengers hurry on and off. A significant share of Helsinki region residents travel underground every day: on a typical weekday, the metro carries 257,000 passengers (HSL, October 2024).
The ceiling offers an example of design’s many functions: 108 lighting domes act as acoustic dampers, illuminate the platform, and conceal speakers and sprinkler nozzles.
Aalto’s research fields and alum expertise are visible everywhere in the underground construction: in technical structures, in the functionality of spaces, and in their atmosphere. In Tapiola, one visible ‘fingerprint’ is Kim Simonsson’s artwork Emma Leaves a Trace. The large sculpture has paint smudges on its palm, and the colours appear throughout the station as if a giant had wiped the walls while passing by.
Recognisable features of each station help passengers orient themselves. If the stations flashed by identically, the underground could feel far more claustrophobic.
The West Metro is more than a means of transport: it was a major urban development project. In his 2019 doctoral thesis, Oskari Harjunen – now an assistant professor of real estate economics – found that prices of older apartments near metro stations rose by 4–5% due to the metro even before operations began.
To isolate the impact of the metro, he compared prices to similar areas not affected by the project. ‘The housing market looks ahead. When there’s enough certainty about a major investment, the expectation becomes capitalised into prices,’ Harjunen says.
The metro transforms the city in ways beyond improving connections. By increasing transport capacity, it enables the construction of more housing around stations, which in turn attracts more services and can further increase an area’s desirability.
As part of a Helsinki-region research collaboration, Harjunen is studying how the metro has affected travel behaviour and whether it has reduced car use. Researchers have access to datasets such as vehicle inspection records, which are processed so that individuals cannot be identified. They are also examining the metro’s effects on companies and their productivity.
‘Large rail-transit projects are planned across the region. Research gives valuable insight into the kinds of impacts to expect and greatly supports cost-benefit analyses.’
On a weekday morning, Helsinki’s Forum parking hall is quiet, with plenty of empty spaces. Many of the city’s parking caverns, metro stations, and sports facilities also serve as civil-defence shelters – this enormous hall included. The thick steel doors can withstand shrapnel, pressure, and gas, and the equipment is mounted on springs to absorb shock.
Life in the capital region extends deeply into the bedrock. Underground, people lift weights, swim, skate, shop and eat, and enjoy culture – from Amos Rex to Espoo’s Kannusali. Out of sight lie other essential functions: a wastewater treatment plant and a combined heating and cooling facility.
Why does it make sense to build underground? First, it’s about building where it’s possible. Professor of urban economics Tuukka Saarimaa says one motive is that urban space is limited and high-rise construction is restricted. ‘If Helsinki wants to maintain a relatively low skyline and demand for space is high, underground construction may become viable even though it’s expensive.’
Parking regulations matter too: the city requires a certain number of parking spaces for residential buildings, though Helsinki recently removed the requirement across a large part of the downtown area. Parking-hall costs feed into housing prices.
‘In some areas, mandatory parking may limit housing supply – fewer homes get built than would be if parking weren’t required. People value parking, but you have to consider whether they’re willing to pay what it costs.’
Large infrastructure projects lock in land-use decisions long into the future. Their viability is weighed by comparing costs to expected benefits – such as tunnel-project costs versus shortened travel times, reduced congestion, and improved air quality. These calculations involve uncertainties: for example, estimates for the proposed West Harbour tunnel rely on forecasts of future port traffic.
Underground planning must anticipate future needs despite uncertainty. Helsinki has several ‘ghost metro stations,’ built just in case, because adding them later would be harder and more expensive. The newest reserved space lies beneath Mall of Tripla in Pasila. But no metro is coming there anytime soon – if ever.
Underground tunnels and caves tend to evoke mystery and excitement – especially in Otaniemi, where the local ‘catacombs’ form part of long-standing student lore. Several kilometres of tunnels crisscross inside the bedrock. Below ground lie large civil-defence shelters and VTT’s research halls.
The catacombs – and the fate of ending up there – have appeared in Wappurieha (Wappu celebration) speeches, and over the years students have even held anniversary dinners and ‘sitsit’ banquets inside the rock. Real and embellished stories tell of mishaps and odd twists of fate underground in Otaniemi. For some students, the appeal stems from their studies in rock construction, minerals, and geology – but perhaps most are simply drawn to these intriguing spaces.
In Ossi Törrönen’s 1991 story collection Ossin parhaimmat lässyt (~ Ossi’s best pranks), the ‘atom cave’ appears in many legends. One tale involves ‘Nordic police chiefs driving Porsches in the atom cave,’ stemming from a PR officer’s desire to entertain visiting police leaders with a student prank.
There was even said to be a small underground lake for a while, presented to visiting Swedish students as a ‘miracle spring.’ One student demonstrated its powers by wishing, ‘Jag vill gärna ha en flaska öl.’ The guests watched in astonishment as someone emerged from the water like the sea monster Iku-Turso, not with a single bottle but with an entire crate of beer.
Text: Terhi Hautamäki. Photos: Alexander Komenda.
This article has been published in the Aalto University Magazine issue 37, February 2026.
Built over decades, Finland’s civil defence shelter system covers almost the entire population and has cost the equivalent of three years of defence spending.
