The sound mirrors are passive devices used to reflect and concentrate the acoustic waves: they are widespread along the South and East coasts of England. They consist of concrete parabolas with a diameter of a few meters. In the twenties of the last century, their use combined with microphones, allowed to intercept planes directed towards the coast, discovering in advance any possible attacks. The need to be positioned near the coasts mainly in raised areas, the strong materiality of the concrete and their huge dimensions make them spectacular and extremely fascinating structures, able to dominate the entire surrounding landscape. These last thirteen acoustic mirrors are a rare testimony of a wise use of acoustic physics combined with an incredible mastery of materials. Their evident state of abandonment, not only physical but also of memory, makes us reflect on the obsolescence of a technology based on the direct fruition of reality, in a society in which, paradoxically, representation seems to have replaced reality itself.