The perennial sound installation entitled "Niches Acoustiques", a winning project of the Participatory Budget of the City of Paris, is dedicated to an urban public space: the square of the new courthouse (Tribunal Judiciaire) of Paris, located in the north-western part of the capital. This square represents a complex challenge: serving a landmark building while at the same time being part of the development of a new urban neighbourhood. The installation, a work on spatial listening and perceptual sound masking which is currently being composed, contributes to shaping the identity of this new public space. It creates an appeasing and varied auditory foreground that sends annoying monotonous noises into the background while opening up the courthouse square to an urban narrative that connects the territories rather than separating them. This installation is a winning project of the Participatory Budget of the City of Paris. During this presentation, I will introduce the development/context and the detailed artistic proposal of "Niches Acoustiques" and address specific challenges related to the creative process of what might be called non-intrusive urban (land) sound design. I will situate this work within my artistic research at IRCAM-STMS, which investigates methodological questions of composing in(to) existing sonic environments. This investigation also led to the scientific and artistic collaboration applied to the "Niches Acoustiques" project, currently implemented within the Perception and Sound Design team in the framework of Valerian Fraisse's thesis on the information and evaluation of public space sound installations.