Delirious Porto: Porto's new concert hall is a conspicuous urban presence that proclaims its otherness, but has inventive moments.

So, finally, Delirious Rotterdam comes to Porto; another city ticked off, another destination label pasted on the well-travelled OMA valise. With delicious irony, the new Casa da Musica was inaugurated by a Lou Reed concert, drawing irresistible comparisons between Lou and Rem as twin punk godfathers refusing to grow old gracefully. Posing moodily on its inhospitable travertine plaza, the Casa radiates textbook punk insouciance, its ugly, sub-Breuer geometry, weirdly flat surface and brute scale squaring up purposefully to the city that spawned it under the cosy aegis of the 2001 European City of Culture. Catalysed by the cultural spotlight, Porto decided that it needed a modern concert hall capable of coping with a protean repertoire and, in 1999, OMA won a limited competition with its provocative proposal; solid yet light, big yet intimate, aloof yet connected, a statement music box for the twenty-first century.

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Widely touted as Porto's Guggenheim, the Casa da Musica is a similarly incongruous sprinkling of superstar fairydust in a city not given to grand or empty gestures. Unlike poor, obscure Bilbao, however, Porto is not in need of the international ministrations of Guggenheim Inc to put it on the short break map. It has great topography, hearty cuisine and colourful heritage. It is hardworking and unpretentious. 'Coimbra studies, Braga prays, Lisbon shows off and Porto works', goes the Portuguese saying, and for decades this has found reflection in the Porto School which champions less voguish values such as reticence, sobriety and regional nuance. Nuance, you sense, is not in the OMA lexicon, though irony clearly is. One of the minor themes of the Casa is a knowing take on the Portuguese use of ceramics. The VIP suite, for instance, is surfaced in white tiles lovingly hand painted with florid blue motifs in the traditional azulejo manner. But, thankfully, Rem has resisted the temptation to go for Grayson Perry-esque tableaux of sex and violence and stuck with rural idylls and gentlemen being courtly in frock coats.

This is about as regionally nuanced as the Casa gets. Claims are made for the building's huge mass as being somehow Iberian (even like Siza), but no Portuguese building that size was ever so singularly unrelieved. Flatness is all, with the pale grey epidermis of the concrete peeled away in places to reveal supersize frameless vitrines. Despite being obviously skilfully cast with panels on the diagonal, the concrete just looks bare and unfinished, its oppressiveness exaggerated by the building's scale. You also fear for its capacity to weather gracefully in one of the wettest parts of Europe, though OMA are confident that a special coating will efficiently throw water off the surface, via gutter-like joints between the panels.

The demotic plainness of materials and crudeness of form contrive to enhance its aura of otherness. 'Meteorite' is becoming a tiresomely overused metaphor, and May's Domus enthusiastically plays the 'it-came-from-outer-space' game with shots from a helicopter showing a meteorite's eye view as it tracks in on Porto. From the air, you can make out the Douro where it meets the Atlantic and the precise circle of the Rotunda da Boavista, with its trees, benches and towering war memorial column. Boavista is a relatively well-heeled district, but around the OMA site any sense of civic continuity peters out into scruffy backstreets, vacant lots and car parks.

Marooned on its bleak travertine plaza, the Casa is fashionably disconnected from its surroundings, like a giant abandoned television that's been knocked about a bit. Round the plaza edges is an artificial topography of rolling mounds that will be energetically colonised by rollerbladers (you can imagine them merrily scything down people coming out of Vivaldi concerts; perhaps part of the punk gameplan to epater les bourgeois). But with this carefully cultivated sense, the building could be anywhere. This is hardly surprising. Its challenging form, we are told, was arrived at by simply inflating to the power of five an earlier unbuilt project for a trophy house based loosely on the principles of carving voids out of a solid mass. Though some critics see this as an example of the fecund creativity of the OMA atelier; where no intelligence is squandered, it does seem a decidedly lazy and disingenuous way of making buildings.

Such a self-referential approach, however, has again proved a forcing house for structural wizardry, conjured by Arup magus Cecil Balmond. A 400mm thick faceted concrete shell supports and ties the building together as well as acting as an internal stiffening diaphragm. At the building's core, I m thick auditorium walls provide additional stability and anchor the composition. Perhaps iceberg is a better metaphor than meteorite, as the Casa is almost as large below ground as above. Under the plaza is a subterranean netherworld of dressing rooms, rehearsal spaces, offices and parking, to keep the upstairs show on the road.

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As has become the case with OMA buildings, the Casa is defined in formal and experiential terms by a looping, swooping circuit that threads together the principal spaces--large and small auditoria, foyers and bars, education and cyber music rooms, and finally the restaurant and terraces on the top floor, where the sense of carved space is possibly most clearly articulated. This circuit begins in the plaza, with a processional staircase that sweeps up to the piano nobile entrance level. From the main foyer it then cranks and kinks through a series of promenading spaces that resemble, like most OMA interiors nowadays, a set from The Cabinet of Dr Caligari in their vertiginous, Expressionist angularity.

At the heart of the music box is its showpiece, the 1300 seat auditorium, intended to be equally at ease hosting acid jazz or the Porto Philharmonic. Perpetually trying to reinvent the wheel, OMA allude darkly to the 'tyranny of the shoe-box concert hall', but are forced to concede that both functionally and acoustically, it is still the optimum solution. (Though you can practically hear the teeth grinding in the press material.) So what to do? The answer is simply to make the short ends of the hall transparent, infilled with huge panels of vertically corrugated glazing (the corrugations soften the glass for acoustic purposes). This is actually a genius move in chat it does not compromise the auditorium's physical form or acoustic efficiency, yet radically re-envisages its essential character, exorcising hermetic, nocturnal insularity and introducing light and views. Framed and filtered in the huge rippling vitrine behind the stage is the Porto skyline and the trees and column of the Rotunda da Boavista. The city becomes the audience. Slightly less inspiringly, the other glazed end, which houses the main bar, overlooks a scrubby car park. But still, the rulebook has been deftly rewritten. Glare is mitigated by cunningly layered and knotted nylon blinds that resemble oversized net curtains, made by Dutch designer Petra Blaisse. Other similarly glazed slots cut into the sides of the hall connect it visually with the surrounding promenade spaces, so you are constantly and voyeuristically aware of the building's main event.

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In another subversion of history, hinting at the gorgeously overblown gilded interiors of Portugal's Baroque churches, the hall is lined with plywood panels hand embellished with squares of gold leaf to create an enlarged, pixellated 'supergrain' effect (but which actually looks like a trashy zebra print). The ornate Iberian Baroque organ is, predictably, a fake, but a real one may materialise when funds permit. Texture and colour are applied with abandon--the audience snuggles down in plush silver velvet seats with squashy latex arms, private boxes have doors of padded gold lurex, and the smaller auditorium, which can seat 350, is lined with panels of perforated plywood stained oxblood red. Yet after the starkness and inanimation of the exterior, this super saturated sensory overload is at times overwhelming.

What, then, to make of Delirious Porto? When researching a special issue on Portugal last year (AR July 2004), I was struck by a comment from Fatima Fernandes, a local Porto architect, 'The sons have too much respect for the fathers', implying that things needed loosening up. And this is happening, with or without a musical Guggenheim and a new punk godfather. Porto is a much more porous architectural scene than it was, say 10 or 20 years ago. An emerging generation is finding its own voice, exploring the world, exchanging ideas. OMA have produced a clever, fashionable building, but one that, especially as an urban proposition, is not easy to like. What will be interesting is whether such international posturings are unthinkingly replicated (God help us) or tempered by the Portuguese condition of 'critical scarcity' and transmuted into something altogether richer and more resonant. Delirious regionalism, perhaps.

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