For the competition, reinvent Paris – Les dessous de Paris – the Compagnie de Phalsbourg invited Razzle Dazzle to design a building to house a unique recreational and cultural facility for children and their families. Structured around the theme of learning different knowledge such as gastronomy, nature, digital culture and mythological knowledge, this programme aims to transmit to our children the fundamental knowledge as well as the knowledge of tomorrow. As an extension of the Parisian greenbelt, the site of the former Auteuil train station offers the possibility of underground development, underneath the Boulevard de Montmorency for the underground level, and in the upper part, at the level of the nature trail. The architectural intervention we propose aims to make the link between these two levels while meeting the challenge launched by the City of Paris: “to reveal the great potential of underground spaces that are usually neglected”. To do this, like the parcel, the building’s layout, all in length and depth, is carried out on a northeast/southwest axis, but also on a vertical axis, seeking to create physical, visual and poetic interconnections between the city and the trail. As a first step, two openings are made in the existing retaining wall to allow direct access to the underground part of the building. In a second step, like a plant, a set of juxtaposed greenhouses emerge on the surface. To the south, the first greenhouse, bathed in light, looks towards the Porte d’Auteuil. The second, overhanging above the existing staircase, marks one of the main entrances to the public. The next two greenhouses, set back from the retaining wall, maintain a link between the city and the nature trail, free up a patio at street level while providing essential natural light for the ground floor. Finally, the last volume, facing both the city and the nature trail, results in a half greenhouse whose facade on the trail can be fully opened, allowing the park to enter the heart of the building.