The perception of the underground of cities may well raise concerns at first, as we imagine it dark, damp and uncomfortable. But if we go beyond this fantastical prejudice, we will find another image of the underground, one that is more physical and sensitive. The Groundscape offers a potent catalyst for urban networks, a naturally ideal thermal inertia, an unrivalled respect for the landscape, an elegant enhancement of our architectural heritage, and a unique palette of lights. The Groundscape is an underside of the world, it is what we would see when diving if the ground was like the ocean and cities like vessels on its surface. The Groundscape is a landscape of a different nature, which extends the latter and broadens our world.