THE St Magnus Festival can usually be relied upon to produce something imaginative and enterprising for its core annual event that features members of the community. In fact, wondering what they are going to turn up next has become a major intrigue in anticipation of each year's programme.

And, true to form, they have once more produced the goods in a fascinating, puzzling, and occasionally exasperating show called Sunnifa. Is it dance? Is it theatre? Is it performance art? Is it installation art? There's no single answer to those questions - though the good folk of Aberdeen can have a stab at it this weekend as, quite exceptionally, this particular Orcadian extravaganza will travel to the granite city.

In fact this show is breaking new ground for the St Magnus Festival in that it is effectively a collaboration between Orkney and the city of Aberdeen, bringing together dancers from both areas under the tirelessly enthusiastic direction of Andy Howitt, now a fixture in the north and one of its most energetic animateurs.

Howitt's latest choreographic howitzer was born out of his last for the festival - the monumental Orkneyinga, which deployed hundreds of locals in a series of locations for site-specific performances of the ancient sagas.

Following that, there was a realisation among the festival's directorate (manifested also in a demand from the people who had been involved) that an enormous number of skills and techniques had been amassed and risked going to waste.

Never ones to miss a trick, the Orcadians met with Howitt and put together an application for a #15,000 lottery grant to bring the choreographer to the islands on a regular basis and develop further those skills through workshops and projects.

Additionally, the money (which they were awarded) would finance a specific project for this year's festival. And so, following extensive research by Howitt, was born the tale of Sunnifa, wonderfully appropriate to the location and harnessing the abilities of a team of Orcadian and Aberdonian dancers - non-specialists all, though you would never guess it from their intricate, sweaty, and complex choreography: more like a combination of ritual procession and mobile body sculpture than orthodox dancing.

The tale itself has two strands. Sunnifa (or Sunniva) was, in Norse legend, an Irish princess who fled her country to escape marriage. She settled on an island with her followers, all of whom were buried in a landslide. A century later the natural tomb was opened and the body of Sunnifa was found intact and wholly preserved.

That's the legend. Now the facts. Since that time three ships have been named after the princess, the first in the nineteenth century, which ran aground off Aberdeen and broke up in 1930.

The second, which did war service in the arctic convoys, was presumed to have become encrusted with ice, turning turtle and leaving no survivors. And the third, built in 1972, is still in service (strikes allowing).

Instead of attempting any narrative setting, Andy Howitt has woven a conflation of fact and legend into what he described as ''a fantastical blend of the real and the unreal'': an eerie and often beautifully evocative performance. There is slow motion, underwater choreography, the straining, intensely claustrophobic suggestion of entombment, and a bewildering array of combinations of dancers, from sculpted ensemble to the twisting counterpoint of three bodies locked together, to individuals in solo flight.

It's all set in a grid-like installation - resembling a board game with the parameters marked by tapes which are drawn out, stretched, and curved into a thesaurus of evocative shapes - all devised by artist Anne Bevan.

And the ingenious sound world which surrounds and pervades the arena is entirely on tape. Constructed by Aberdeen composer, Pete Stollery, it sounds like an electronically-generated score, but it ain't. All the sounds are real - from myriad depictions of water and waves, to the incredible sonic suggestion of an icy chill, to the thrum of a ship's engine; all sampled and treated sounds, many of them recorded in Stromness Harbour.

Staged in the Orkney Auction Mart (home to cattle and furniture auctions, as well as local raves) the whole thing was a touch overlong, and occasionally puzzling in the simultaneity of its images. But it's highly original, and - musically, sculpturally, and choreographically - entrancing and intriguing. See it at the Lemon Tree on Saturday.

Meanwhile, plans are already afoot for next year's extravaganza in which - hints festival director Glenys Hughes - the Orcadians, with an eye on the approaching millennium, are going to leap back in time a couple of thousand years and go Greek with a play, upon which, I have no doubt, they will lavish all their enterprise, from original music to a distinctive setting.

But not all of the enterprise this year is limited to the Orcadians. The BBC Scottish Symphony Orchestra, currently riding very high in the Scottish charts, and playing up a storm in Orkney with conductor Martyn Brabbins, are keeping all and sundry entertained with their unrivalled social skills.

But one group of eight players, which has detached itself from the orchestra, has provoked hilarity and (because of the unpredictable weather) incredulity among the islanders by going native and setting themselves up in a field with a battery of tents.

A midnight visit to this tribe confirmed that - as ever with the SSO - they do things in style. As well as the expected (and inexhaustible) supplies of liquid refreshment, there is a host of mod cons, not least a pink inflatable two-seater settee and fresh fish supplied daily by another three members of the orchestra who, directly from the concerts, indulge their own passion by heading out for all-night fishing. See the SSO? See enterprise?

n Sunnifa: The Lemon Tree, Aberdeen, Saturday, 3pm

and 7.30pm.