At a glance, the formal trajectory of the work is extremely simple, the title immediately revealing to us the key to the "mystery". The "Forbidden Gardens" is, at the heart of the composistion a piece of music taken from a chorale (Herzlich für mich erfreuen) by the German composer Samuel Scheidt (1587-1654).
To get there and "see" these "forbidden gardens", Pousseur employs a system of windows, strewn through with music deduced from Scheidt's work. The formal curve of the work therefore highlights a play of inclusions of the past through the windows (i.e. the transformed extracts of the chorale) interrupting with increased frequency a discourse with modern appearances (clusters, flutter, various attacks, etc.) recalling by certain techniques used (harmonic filtering), the electrosacoustic background of the composer. Gradually, these inclusions gain in importance and eventually drive out the other music which gradually dissolves, never really having seen the light of day. Once the chorale is spoken, this in turn disappears with a game of inclusion similar to the one at the beginning, but this time it is the other music that comes to interrupt its progress.