I want you to think of an example of underground infrastructure.

No matter your background or expertise, it’s likely that your mind immediately went to something that provides a critical service to those of us above ground. Perhaps you thought of a rail or road tunnel. Perhaps a network of water and waste pipes, or dense bundles of electricity or telecommunications cables. While this picture of the underground as a service layer for an overlying urban form will feel familiar to many, in reality, it belies much of what that realm has meant to us throughout our history.

For example, did you know that the festival of Halloween traces its roots to a singular cavern in Ireland? Or that the Moscow Metro was a key propaganda tool in the 1930s? What about the permafrost-clad facility that is home to more than a million crop samples?

Humanity has always looked to subterranean spaces, and our relationships with them are as rich and diverse as the cultures who call this planet home. As we move into an increasingly urban future, we will undoubtedly demand much more from the ground beneath our feet. Reaching beyond the obvious – to those surprising and lesser-told stories of the subterranean – may yet provide the inspiration and ideas we seek.

Mythology and mystery

Image credit: Robert Mulraney, www.cavesofireland.com

From ground-level, Oweynagat is unassuming. This is how writer and documentary-maker, Manchán Magan described the entrance to the cave on his first visit, “A hawthorn bush grew from its top, and under it, amid a tangle of brambles, nettles and grasses, was a stone with what looked like a foxhole or the entrance to a badger set beneath it.”[1] Nestled near the edge of a field in a rural part of northwest Ireland, Oweynagat is part of what was once an extensive royal settlement – the hub of the ancient Irish kingdom of Connaught, dated at 5,500 years. Legend has it that it was home to an immortal queen called Morrigan and her three wildcats, which gives the cave its name, Uaimh na nGat (Cave of the Cats).

Every year, on the festival of Samhain (October 31st) these creatures, and the many others believed to inhabit the underworld, escaped into the world of the living, via the cave. People gathered at Oweynagat lit fires to protect themselves from the darkness, disguised themselves as fellow ghouls, and carved faces into turnips. While the site gradually fell into disuse, Samhain remained a key date in the Irish calendar. And in the 1800s, those traditions, carried by emigrants, began their metamorphosis into what we now call Hallowe’en.

Oweynagat’s story isn’t entirely hellish. According to Magan, at other times of year, it was a chamber “…of transmutation.” A destination for those seeking “…spiritual and psychological exploration.” There are countless examples across cultures of underground spaces playing this dual role – a place of both darkness and light, of birth and death, and a portal to another land. Several Native American nations, including the Madan and the Hopi, trace their origins to subterranean realms. For Hindus, the underworld is a home to powerful gods, and Māori lore suggests that the underground movements of the god Rūaumoko is the source of New Zealand’s tectonic forces. For Christians and Muslims, traversing down into the Earth is linked with fear and punishment. For other faiths, underground chambers have long helped believers commune with their gods.

These associations with the underground are very relevant to current discussions around urban planning. In a paper published in 2017, psychologist Dr Eun Hee Lee looked to a future in which we’d see an increased use of subterranean spaces for meeting our everyday needs, like commuting, socialising and habitation.[2] Her focus was on the psychosocial factors associated with underground environments, because, as she writes, “The ways people think, feel, and behave are closely tied to individuals’ bodily interactions with the physical environment.” One of the four key factors that she identified was “negative culture-based associations”, i.e., linking underground spaces with death, fear, superstition, and poverty. She contends that overcoming this will involve “Re-conceptualisation…One way to improve the perception is to broaden the usage of underground spaces while putting emphasis on the privacy and protection that they can offer.”

Artistic pursuit

Stadion station, Stockholm metro. Image is CC BY 2.0: https://www.flickr.com/photos/62405357@N03/34578408935

Sheltered and subterranean environments have long been safe places for humanity to explore its creativity. Ancient imagery adorns walls at numerous sites across the world – everywhere from Australia to South Africa, and Indonesia to South America. They are a reminder that we have always left our mark on our surroundings. The Cueva de Ardales – a cave in southern Spain – is home to the earliest example of rock art so far discovered. The site contains over 1,000 prehistoric paintings and engravings. One set of images, consisting of dots, finger prints, and hand-stencils, all created with red ochre pigment, is especially important. It has been dated to at least 64,000 years ago, which suggests the images were created by Neanderthals. In 2022, researchers showed that the same cave was used as a canvas for artwork and as a burial place for more than 50,000 years[3].

Underground spaces are still widely used by artists from all backgrounds – contemporary examples include Ra Pualette’s hand-carved sandstone cave, Herbert Baglione’s haunting ‘shadow art’ in abandoned bunkers, and iconic graffiti-filled tunnels like Leake Street in London, Tunnel des Tuileries in Paris, and Freedom Tunnel in NYC. Museums, dance schools, and recording studios also increasingly make use of subterranean spaces.

Metro stations have become another playground for design and architecture. In the book, Underground Spaces Unveiled, authors Han Admiraal and Antonia Cornaro write about the opening of the Moscow Metro in 1935.[4] The grand designs of the stations were “…a socialist reaction to the dull, drab and uniform systems of the West.” With high-ceilinged halls, ornate lights, and floors covered with reflective marble, they served “…a propaganda purpose in their explicit grandeur, creating an atmosphere that would negate any negative feelings of being underground.” In addition, the distinctive appearance of each station acted as its own wayfinding tool, which meant that passengers unable to read the station name could still recognise it from inside the metro car. That point inspired two Swedish artists to successfully campaign for the introduction of art onto the Stockholm Metro in the 1950s. Today, more than 90 of the network’s 110 stations feature artworks, with each station retaining its own distinct design. It is now considered the world’s longest art gallery.

When viewed in the context of Lee’s psychosocial factors research, these projects offer some interesting insights. Lee identified “isolation” – i.e., limited access to the outside world – as a key factor that influences our experience of underground spaces. Increasing the number of connections between the underground and the surface, as well as using large passageways that mimic streets, “…can promote a sense of familiarity from users.” In addition, the construction of lightwells, as well as the use of clever lighting can help underground environments feel more like the outdoors. The third of Lee’s factors is “perceived control”, related to the absence of windows, landmarks, and greenery. Recent research from the University of Hong Kong shows that efforts to improve air quality in underground spaces, in addition to the use of virtual windows, can greatly alleviate some of these concerns.[5] And Admiraal and Cornaro write, “…. creating distinguishing features that provide visible cues and add to the enjoyment of underground spaces should be used, as opposed to uniform designs of stations along a route.”

Scientific endeavour

Large Hadron Collider. Image by CERN (CC-By-SA) https://en.wikipedia.org/wiki/File:Views_of_the_LHC_tunnel_sector_3-4,_tirage_2.jpg

175 metres below the Jura Mountains is a tunnel. It is a ring, 27 km in circumference, with a slope of 1.4%.... and protons can travel through it at close to the speed of light. That’s because this tunnel is home to the biggest machine ever built: the Large Hadron Collider (LHC), a research facility run by the European Organization for Nuclear Research, known as CERN. For almost 15 years, international teams of scientists have carried out experiments on the LHC to probe the nature of our universe by studying its fundamental building blocks.

Scientists searching for neutrinos also have to travel deep underground to find answers. These ghostlike, subatomic particles ejected by our sun (and other stars) barely interact with ordinary materials. Catching one involves constructing huge tanks filled with a fluid – often a dense form of water – in subterranean caverns. Some detector tanks can hold the same amount of water as twenty Olympic swimming pools. Their size increases the tiny probability of the elusive neutrino making an appearance. And by doing this research underground, scientists make use of the overlying rock to ‘filter out’ the other particles that continuously rain down on our planet.

Believe it or not, botanists and agronomists also work in subterranean facilities. Rather than hunt for particles, these scientists are safeguarding the genetic diversity of the world’s crop supply, in the face of various threats. Described as “Noah’s Ark for seeds”, and currently home to 1.2 million samples, the Global Seed Vault can be found 152 meters inside a mountain on Svalbard in the Arctic Circle. Its remote location was chosen because it offered “almost perfect conditions” for long term, secure seed storage. The presence of permafrost provides temperatures of -5 °C, which means that the seeds, sourced from a network of gene banks all over the world, will stay frozen, even in the event of a power cut. In addition, cities like Taiwan, Seoul, and London are transforming vacant metro tunnels into vertical farms, where they grow salad leaves and microgreens to sell locally. Vertical farming has the added bonus of bringing greenery into underground spaces. For Lee, “Such a measure will promote the physical and psychological well-being of the underground community.”

Projects like these push the boundaries of tunnelling in numerous ways. For a start, there are no standard rules or guidance for the design of underground research facilities. Each one is bespoke, with its own unique set of requirements. The same is true for monitoring and maintaining the facility once it has opened. To meet this need, CERN has developed its own robots that can capture data and photos from the tunnels, and an algorithm that identifies cracks and other features in real-time. They’re also exploring the use of fibre optic cables to remotely measure underground movements. This would allow them to continuously monitor the tunnels, even when an experiment is underway. These tools look set to find widespread use in other tunnel projects.

CERN’s scientists hope to add another underground facility to the site in the coming decades, which will house the next generation of particle collider. As well as pushing the boundaries of science, this project would involve the construction of a 100 km-long tunnel. That’s almost twice the length of the Gotthard Base Tunnel, which currently holds the title of ‘world’s longest tunnel’.

Refuge

DERINKUYU. CC3.0. Attribution: Ahmet KAYNARPUNAR https://commons.wikimedia.org/wiki/File:DERINKUYU_UNDERGROUND_CITY_-_panoramio_(2).jpg

Cappadocia lies in eastern Anatolia, in the heart of what is now Turkey. An internationally-recognised Geological Heritage Site, its high-altitude landscape is dramatic, peppered with multistorey cones and chimneys of pale pink volcanic rocks. The region’s geology goes some way to explaining why it is also the site of a large number of ‘underground cities’, including the most sophisticated, Derinkuyu. The city’s network of tunnels and caverns, carved into the soft rock, acted as a stronghold in times of war and other crises, and as an everyday storage facility and transport link. Each of its exits was marked with a massive stone door that, when needed, could be rolled into place from the inside of the tunnel. The presence of extensive ventilation shafts, wells and rainwater tanks suggests that the city was designed to be self-sufficient; a characteristic that was put to great use during the Arab–Byzantine wars. Excavated to a depth of 85 metres, and split over eight levels, Derinkuyu was large enough to have temporarily housed 20,000 people along with their livestock.

It’s possible that Derinkuyu was a source of inspiration for another underground metropolis; this one built in anticipation of a nuclear war that (thankfully) never happened. Between 1969 and 1979, a vast network of tunnels and bunkers – covering an area of 85 km2 – was constructed beneath Beijing’s city centre. Called simply the ‘underground city’ (Dìxià Chéng), it was equipped with a wide range of facilities, including restaurants and factories. It had an elaborate ventilation system too, as well as gas- and water-proof hatches. According to one account, the city was designed to safely house half of Beijing’s population for 4 months. Though Dìxià Chéng was never used for its intended purpose, parts of it went on to become low-cost housing and office facilities. In 2017, National Geographic reported that more than a million people were living in these former bunkers.[6]

While some underground cities were purpose-built, there are also countless examples across the world of existing subterranean structures being repurposed into places of refuge. They include Naours, a chalk mine in northern France, that sheltered people fleeing conflicts from the Middle Ages through to the 17th century. The London Underground tunnels provided vital protection to city-dwellers during the first and second World Wars. And even today, residents in Coober Pedy – an opal mining town in the centre of the South Australian desert – live in underground homes in disused parts of the mines.

On first glance, this view of subterranean spaces as a safe haven seems somewhat at odds with Lee’s fourth and final psychosocial factor; “perceived security”. But as she explains, security has a very specific meaning in this context, “[it] refers to risk or dangers stemming from human behavior (such as terrorist attacks, crimes, etc.)” She also says that a lack of landmarks “…may provide an opportunity for those with a criminal intent.” In order to avoid these associations, she urges designers to think carefully about visibility, lighting, wayfinding and surveillance in underground environments.

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So, what might all this mean for the future of our cities? The potential answers to that question are on a sliding scale. At one end of it, you’ll find a lot of hype (and the occasional misleading headline) that suggests we’ll all soon be living full time below ground in inverted pyramids, emerging only for the occasional outdoor activity. At the other end of the scale, there are those that view subterranean spaces solely as a service layer – a place to hide all the inner workings of an urban centre; not somewhere humans should be spending their free time. It’s likely that the reality lies somewhere between those two extremes; an increasing proportion of facilities will move underground, to preserve ‘topside’ space for housing and ecology. That’s certainly the vision that Singapore is extolling. Its subterranean masterplan, first published in 2019, involves moving all utilities and many transport networks underground, as well as industrial warehousing, datacentres and fuel storage.[7] Speaking to Reuters, Ler Seng Ann from the Urban Redevelopment Authority (URA) said that this will “… free up surface land for housing, offices, community uses and greenery, to enhance liveability.” [8]

There are obvious benefits to adopting subterranean architecture – thermal conditions being one of them. Cities that experience cold winters like Helsinki and Montreal already have numerous recreational facilities underground, linked via pedestrian walkways. Swimming pools, running tracks, retail outlets, hockey rinks, theatres, museums, karting tracks, and churches can all be accessed and enjoyed, even at temperatures of -15°C. With climate change making weather events increasingly unpredictable and extreme, weatherproof refuges like this may become more important to urban-dwellers. There are challenges to going underground too, not least the provision of basic utilities like water, waste, and clean air. And, as highlighted by Dr Eun Hee Lee and others, there are a number of psychosocial considerations – some positive, some negative – that need to be accounted for

Moving to a more underground future will require careful planning, cross-discipline cooperation, and a firmly human-centred approach. And what could be more human than learning lessons from our past?

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References

[1] Page 66, Listen to the Land Speak, by Manchán Magan. ISBN: 9780717192595

[2] A Psychosocial Approach to Understanding Underground Spaces. Front Psychol. 2017; 8: 452. DOI: 10.3389/fpsyg.2017.00452

[3] The nature and chronology of human occupation at the Galerías Bajas, from Cueva de Ardales, Malaga, Spain. PLOS ONE, 2022; 17 (6). DOI: 10.1371/journal.pone.0266788

[4] Pages 132-135, Underground Spaces Unveiled by Han Admiraal and Antonia Cornaro. ISBN: 978-0727761453

[5] Enhancing underground development users' health through facilities management: a study of the underground metro system in Hong Kong. IOP Conference Series: Earth and Environmental Science, Volume 703 DOI 10.1088/1755-1315/703/1/012043 https://iopscience.iop.org/article/10.1088/1755-1315/703/1/012043

[6] https://www.nationalgeographic.com/photography/article/atomic-rooms-beijing-china-housing

[7] https://www.ura.gov.sg/Corporate/Get-Involved/Plan-Our-Future-SG/Innovative-Urban-Solutions/Underground-space

[8] https://www.reuters.com/article/us-singapore-landrights-planning-idUSKCN1ON01J

Laurie Winkless

Surprising stories of subterranean spaces