For a small percentage of people, the mere thought of being underground in a confined space can be terrifying. Gunnar D Jenssen, who researches underground psychology and space design for Scandinavian research organisation SINTEF has found about 3% of people are severely claustrophobic – not having a clear way out or being fearful of flooding or fires can cause a lot of stress. But there are some way to counter their fears.

“If you give these people something that gives them perceived control over the situation, they accept being in it. That is the key. Transferring that into architecture, into design is the line of work we’ve been following.

“The basic things you have to have there is clean air, you have to have the space, it has to be spacious or perceived [to be] spacious. You can use illusions but the best is if it really is spacious and [has] good lighting.”

Jenssen has worked on four of the longest road tunnels in the world. To create the illusion of space, within the tunnel he creates well-lit oases with palm trees and illusions of the sky along the route. “You go through a dark tunnel and all of a sudden you’re coming out into a bright lit space with trees and plants.

“You have a feeling of breathing space, a feeling of being outside, even though you’re 1,000 metres underground going through a mountain.”