Neither an opera nor a concert work, Nono’s Prometeo of 1985-6 is just the sort of musical ‘experience’ made for festival presentation. More a drama for the ears than the eyes (Nono subtitles it a “tragedy of listening”) it has no action, no real narrative and calls for a large, flexible space to house its multitude of vocal and instrumental groups and live electronics – the ultimate surround-sound event. Originally performed in one of Venice’s great churches and conceived alongside an architectural scheme for a new type of performing space in the form of an upturned ‘ark’, it seemed rather nifty planning for the Ruhr Triennale to be presenting it alongside runs of Monteverdi’s Orfeo, given that composer’s exploitation of similar antiphonal experiments at St Mark’s, and Wagner’s Das Rheingold, itself conceived for a purpose-built festival theatre. Not, as its name might suggest, a festival held every three years, but one that runs in three-yearly cycles under single artistic directors, the Triennale, founded in 2002 by Gerard Mortier and now under the intendancy of Johan Simons, exploits the Ruhr’s industrial heritage to stage work either that simply can’t be squeezed into traditional theatres or benefits from greater space and fluidity of venue. That is certainly the case with Prometeo, and a former power plant in a regenerated, post-industrial landscape park in Duisburg proved ideal.

It may be music theatre without the action, but the drama began half an hour before the start of the performance as handful by handful the audience was invited to follow a bright light through thick fog along the length of the vast turbine hall. Passing through a double-doored airlock into the huge performance space beyond we were faced with a purpose-built labyrinth of seating, where we could choose our own place and wait for things to begin. Two conductors (Ingo Metzmacher and Matilda Hofman) sat waiting to field the music from ten different stages of musicians, set at different heights around the four sides of the hall: four 13-piece instrumental ensembles, a further group of solo players, players of glass bells, speakers, solo singers and a 12-piece choir.

Nono’s treatment of the Prometheus story is almost deliberately obscurantist: he treats his texts – in a mixture of Italian, ancient Greek and German, from poetry and other sources – as syllables rather than words, such that different voices of the choir might sing a whole word’s components one on top of the other. And with no listing of the work’s nine movements in the programme, nor much of an indication of breaks between them from the performers, we were left to absorb the two hours and twenty minutes of virtually uninterrupted music with our ears and eyes alone. In other words it proved easier to understand as abstract expression than attempt to make out its meaning, which one feels only the composer knew.

Nono often uses his extravagant forces sparingly, and despite the passages of space-absorbing tumult that do punctuate the work, the overriding sensation is of quiet beauty, no more so than in the solemn heart of the work, where a solo contralto communes with a handful of instrumentalists as they explore a limited number of held notes. Elsewhere, the choral voices of Schola Heidelberg peppered the piece with its pure-toned rising fifths and tritones motif, vocal soloists rose to the stratosphere of their ranges, instrumentalists of Ensemble Modern explored the extremes of their instruments in volume and pitch and three players struck their suspended glass bells as the live electronic realisation of the SWR Experimentalstudio combined, separated and sent the mixed sounds spinning through the whole cavernous space. It was certainly a marathon for the musicians as much as audience. Although we at least had cushions in our labyrinthine pews, the seating wasn’t made for comfort and there was a steady trickle of departees by the latter stages. But the enthusiasm and dedication of all the musicians were palpable and made their presence felt in the sheer artistry and expressive commitment on show.

The surround-sound was enhanced by subtly changing but monumental lighting design that used the full length of the hall beyond the scaffolding and sheet-plastic screen marking off the performance space from the fog beyond. It was certainly an experience in four dimensions, one that comes to take over one’s being as the performance progresses. And one definitely experiences a different concept of time passing – too slow for some, maybe, but for the bulk of the audience that stuck with it and erupted in applause at the end (a more mature clientele than one usually expects to see at an avante-garde event in the UK) it made for a mesmerising, unforgettable evening, one that will long remain in the memory.