This talk discusses an ongoing research project on the conceptual origins of the Festival Plaza for the Expo ’70. The project examines the so-called Red Book, which conceptualised the spatial and performative scheme to be implemented under the “big roof” designed by Kenzo Tange. It reveals the Plaza as an urban infrastructure generated through the collaboration of computer scientists, musicians, artists and architects among others. The Red Book is a choral testimony of two opposed yet related contemporary trends in 1960s Japanese architectural discourse: the pursuit of computer-controlled responsive environments, and the study of urban cultural practices to assemble and synthesize an archive of urban forms and movements applicable in the Plaza.