Building more sustainably on the ruins of an industrial past that was once vital but has become devastating over time. Here is the challenge that more and more cities around the world are taking up to imagine today bold and resolutely greener construction models. In the north of France, in the mining area, the town of Loos-en-Gohelle has turned into a sustainable open-air laboratory and now dreams of being a champion of ecological transition. But let’s start our journey with Italy and Piedmont, with an astonishing 5-storey residential building where architecture and nature intertwine in an unprecedented way. Singular and avant-garde, the 25 verde stands like a veritable vertical forest in the heart of the city. Right where, historically, stood an old car factory.