Together with Antonia Cornaro, I wrote a book on ‘underground spaces’ aimed at a broad audience and giving an in-depth overview of the subject. Our book is about the future of humanity and its survival. It's about exploring underground space the way we explore outer space. The rationale is the same; the difference is we don’t have to leave this planet to do it. And we can reap the benefits a lot sooner.

The past seven years have seen Antonia, and I travel the world and give presentations, host sessions, take part in workshops and provide training classes. The use of underground space, or rather its lack of use in our cities fascinated us. There is so much that can be done below the surface of our cities. We can get it right, but also horribly wrong. Humans have been exploring the planet from the advent of humanity. From Neolithic flint mines to water tunnels in Roman times. During the Industrial Revolution, humankind discovered how to excavate tunnels mechanically. Travelling through inhospitable mountain ranges with newly invented steam engines led to a transport infrastructure still in use today. 

We have also seen interventions below the surface that were left after the resources being excavated ran out. Throughout Europe, we can find disused salt mines, copper mines, steel mines and coal mines. It was either depletion of the resources that stopped the activity or the lower cost of production elsewhere. Most recently we can see the Netherlands cutting its extraction of natural gas to zero due to the human-induced earthquakes. Many of these activities have been covered and are forgotten, trapped in time and underground space for posterity. Others are given a new lease of life as part of renewable energy systems.

The point of our book is that we genuinely believe underground space has a role to play in the future of our cities. The exciting thing is that there always seems to be a certain duality when it comes to underground space. It can be an asset in providing urban areas additional space when surface space runs out. It can be a foe when forgotten interventions cause sinkholes in urban areas. It can add quality to the urban fabric if done right. At the same time, it can quickly become an urban service layer by placing all uses that require no daylight or that we would instead hide from sight below the surface.

The most complicated and least understood aspect remains the fact that the subsurface, depending on the type of geology, delivers ecosystem services that are key to human survival. This aspect causes the duality between exploitation and conservation. It means that neither a strategy of total exploitation nor total protection is going to lead to sustainable development of the subsurface. The balance between humanity and nature needs to be struck below the surface as much as above the surface.

With our book, we hope to unveil underground spaces to a broad audience of professionals and non-professionals. The reason is that it should be a concern to us all, for all the advantages it can bring to our cities, but also because of the potential risks, it could hold. Foremost we hope that urban planners, policy makers and decision makers will take to heart what we write. The future of our cities could well depend on planning the use of underground space in a comprehensive manner. Only then can we be sure that use is made where possible, delivering the most significant contribution to our cities. At the same time, planning will safeguard where valuable ecosystem services ask for protection and interventions should be avoided.

To speak with the philosopher John Rawls: we all form our opinions and decisions from behind a veil of ignorance. We hope to lift the veil of ignorance that has shrouded underground space for too long. In doing so, we hope that future generations will be able to explore underground space, just as they will remain exploring outer space for the survival of humanity.

Han Admiraal is an urban strategist, thought leader, insights provider and safety consultant. He is co-chair of ITACUS, the ITA Committee on Underground Space and Chair of the Netherlands-Flemish Pipeline Industry Guild. Together with Antonia Cornaro, he wrote the book ‘Underground spaces unveiled: planning and creating the cities of the future’, published by ICE Publishing in London. More information can be found on the book's website www.thinkdeep.net.