LISTEN is a European funded project aiming at creating a new medium: the immersive audio-augmented environment. The concept consists in superimposing a virtual soundscape to the real environment users are exploring. Wireless tracking technology, 3D audio rendering and interactive scenario design allow composing new relationships between sound, body and space. LISTEN developed the concepts and technology necessary to approach this vision and produced audio-augmented reality applications dedicated to media art, museum pedagogy and product marketing. A complete realization of a large-scale audio-augmented reality system for in-door application has been demonstrated and evaluated in public exhibitions at the Kunstmuseum of Bonn. The present document describes the main components of the system architecture, the main features of the artistic and pedagogical demonstrators together with some comments on the design of the augmented world taken from the musical and scientific standpoints.