The slate plinth, like a rugged cliff-face, works pretty well around the front - this is all waste stone, incidentally, the stuff rejected by the makers of roofing slates. It's rather less convincing at the back, where it encloses a big courtyard where a later phase of building will take place. However the helmet/hull bit is wholly successful, its smooth curve serving to conceal the tall flytower as well as housing the elevated auditorium and its foyers. Adams' second big architectural move is to tilt the visor of the helmet forward a little and - instead of putting in conventional windows to the foyers and bars on the various levels - make the windows out of a Cyclopean inscription, in Welsh and English. Each letter is a window. The words are by the poet Gwyneth Lewis. The Welsh ones translate as "Creating truth/like glass/from the furnace of/inspiration", while the English ones say "In these stones/ horizons/sing". The words are arranged across the façade in what was a tricky engineering exercise, since somehow the structure beneath, holding everything up, had to dodge round them.

It makes for an interesting point of arrival - you walk directly under that huge inscription, the riveted plates of the exterior becoming the ceiling of the foyer interior. To your right there is a big galleried timber-clad mall, a bit like a Tudor inn courtyard, with shops and cafes and space for small public performances. The main auditorium, though finished in some unconventional materials such as irregular red gypsum blocks, has a very familiar opera house atmosphere: stalls and two tiers in a horseshoe shape wrapping round the sides towards the proscenium arch of the big stage. The stage is second in size in the UK only to the new Covent Garden, while the feel of the 1900-seat auditorium is more like the London Coliseum. Adams has no problem with either analogy. "We wanted to avoid the drawbacks of modern theatres," he says. The orchestra pit is huge, fit for Wagnerian orchestras and then some, though it can be made to disappear under a thrust stage when necessary. There are areas of flanking seating forming boxes. The seats have solid wooden frames. Traditionalists will not be alienated