Dublin's failure to develop as a major industrial city during the 19th century has meant that the capital's stock of warehouse buildings is far smaller than is the case in equivalent-sized urban centres.

Belfast, for example, has far more such structures, while there are also plenty of examples of warehousing in Limerick, Cork and Galway. But only a handful of substantial buildings of this type exist in Dublin, and several of the most important are associated with the Guinness Brewery.

The enormous expansion undergone by Guinness during the latter part of the 19th century necessitated the construction of a number of new buildings at the brewery, the first of which was the Hop Store, built in two stages between 1876 and 1882. Around the same time, the Brew House was erected and in 1884 came the Robert Street Store.

Impressive as these buildings are, they are surpassed by the Market Street Storehouse, erected at the start of the 20th century and believed to be the very first major steel-framed multi-storey building constructed on these islands; the second was London's Ritz Hotel, on which work began in 1904. When completed, the Market Street building served for the fermentation and storing of Guinness.

Like the majority of the company's other large buildings, that on Market Street was designed not by an architect but by one of the company's engineers, A H Hignett. The designer of the steelwork was Sir William Arrol, whose office was in London, and the builders were McLaughlin and Harvey. Externally and internally, the combined efforts of this team are breathtaking, and not merely because of their technical achievements.

To quote Jeremy Williams again, the store's "arcaded elevations soar upwards, clad with granite and polychromatic brick, held in place by triple-bay corner bastions crowned with machiolated parapets". The only major interruption to the facade is the interjection on one side of a series of giant oriel windows on the first floor.

Inside, the building contained a massive grid of enormous overlapping steel joists and columns, soaring up nine floors to a pitched central glazed roof from which natural light poured into the different sections.

The inspiration for the Market Street Storehouse would appear to have come from the United States and specifically from Chicago, where the creation of such steel-framed multi-storey structures had been taking place for some time. At the time of its completion, one local newspaper remarked "The result shows that, given the opportunity, Irish firms are capable of emulating, and, in this case, excelling the achievements of contemporaries across the Channel and in America, both as regards workmanship and rapidity of execution."

As Sean Rothery comments in Ireland and the New Architecture, the Storehouse "is clearly a building of the twentieth century". It remained in use by Guinness for much of the same century until becoming redundant in the 1980s, when other areas of the company site were utilised.

Thereafter, the building remained empty and, at one time, its demolition was even considered; that this did not occur was due, at least in part, to the expense involved in taking apart such a massive structure. Instead, in 1996, a decision was taken to restore the Storehouse and provide it with a new purpose. Four years, and some £30 million later, that job is almost complete and the building is due to open to the public before the end of November.

While no changes have been made to the Storehouse's exterior - other than the installation of floodlighting - the interior has been considerably reordered to accommodate a number of different services.

It now runs to six floors covering 170,000 sq ft and, in this new guise, the building will act as a visitor centre (taking over from the Hop Store which now has other uses), a training centre for Guinness employees worldwide, a central archive, a suite of rooms for corporate entertaining and - spectacularly installed on the top floors - three new bars.

Inevitably, accommodating all these facilities means the inside of the Storehouse will look somewhat different when it is finished. Nonetheless, certain fundamentals - that basic grid of steel girders and columns - remain quite unaltered.

Given its original designer, there is something entirely fitting in the fact that, while an architectural practice - Robinson Keefe Devane - has been employed on this job, the man responsible for supervising the conversion project, Philip Osborne of Guinness, should also be an engineer.

He has overseen the installation of a central circular atrium which rises the full height of the building to a new glass roof, around which a series of large spaces has been created to meet the requirements of the Storehouse in its new guise.

Visitors will enter from the main doorway and climb to what is classified as the ground floor by means of a relatively narrow escalator, so that on arrival at its summit, the impression of light and space provided by the atrium is all the more striking.

The company's archives (brought together for the first time) will be found on this floor along with a retail and reception area and the first section of a display telling the story of both Guinness and brewing through a collection of artifacts, information panels and audio-visual equipment.

Some of the items on show, not least a pair of American oak vats some 150 years old, which rise up several storeys, are as overwhelming in scale as the building they now occupy.

Nonetheless, it is likely that no matter how excellent the exhibitions and displays, the Storehouse itself will be the feature most visitors will best remember. The conversion is certain to receive widespread approval, although there are occasional disappointments: the atrium is criss-crossed by a series of escalators climbing up to the top storey, cutting across what would otherwise be space of remarkable purity, and a stairwell next to the main entrance is defined by the rather cliched use of glass bricks. Clear glass has been used throughout - for the sides of balconies, for walls between different spaces - in order to allow uninterrupted views of the Storehouse's sheer vastness.

All the steel has been stripped and cleaned before being painted sky blue, its colour when the Storehouse was first built. And where possible, old materials have been reused, albeit sometimes for different purposes; sections of the old steel staircase with oak handrail, for example, now serve as balustrading on different floors.

Many walls are covered by white-enamelled bricks and these have been left in their original state, except in the corporate hospitality suite, where the lower sections of the rooms - rising almost 20 feet high - have been encased for reasons of hygiene.

The floors here are of oak, but elsewhere concrete has been employed, just as was the case in Hignett's original. At this level, the second floor, the Storehouse has enormous windows already offering incredible views across the city; the design of these windows, unchanged since they were first installed almost a century ago, is such that certain sections can be swivelled on a central axis for cleaning purposes.

But for the best views, not just from this building but possibly in all of Dublin, it is necessary to climb to the top of the Storehouse. Within the old structure, Guinness is incorporating two large and interlinked bars, called The Source and the Brewery respectively, as well as a substantial and naturally lit gallery space. Above these again comes the final surprise: an entirely new circular structure which appears to hover over the Storehouse's roof like a spaceship waiting to land. With a steel frame and floor-to-ceiling glass walls, this is Gravity, a Guinness bar with the opportunity to see almost 360 degree views of the city and its surrounding countryside.

Given that the brewery is located at the highest point in Dublin, nothing cuts across the spectator's view from this point and, since the bar will keep the same hours as any other Irish pub, there will be no trouble observing the capital both night and day.

Drinkers sitting on the roof of his building is probably not what A H Hignett had in mind when he first designed the Storehouse, but, given that he worked for a brewery, it is unlikely he would disapprove too strongly of this metamorphosis.