Naughty but nice.

A standard bureaucratic programme has been transformed by architectural imagination into a creative piece of city and a varied and stimulating series of places.

The new local government office block in Munster by Bolles-Wilson & Partner is the result of a 1991 competition and was opened late last year. Like the city's library, completed by the same practice three years ago (AR February 1994), this headquarters for administration of psychiatric services responds to its surroundings with sensitive boldness. But the environs are coarser and simpler than the many-layered tapestry of the inner city in which the earlier building is set.

This one lies on the main east route out of the medieval centre, beyond the green promenade of the old wall ring and the railway (the main European north-south line between Copenhagen and Zurich). Next door, to the east, is a pleasant jumble of nineteenth-century buildings, with offices and apartments over shops; across the street is a large modern version of the same.

The brief called for three floors of cellular offices (the form is mandatory in the German state services), shops on the ground floor, and a cafeteria on the roof which could be used for private functions and jazz concerts- a decent, mixed urban recipe (in how many other countries would you find the bureaucracy anxious to open its office buildings as places of entertainment for the general public in the evenings and at weekends?).

But both site and programme posed problems. The west end is adjacent to the busy railway, with only a few trees in between. And the narrowness of the plot meant that the building had basically to be long and thin, though the architects were determined at all costs to prevent the dead monotony of a bureaucratic slab running parallel to the thoroughfare. By manipulating site geometry, they have evolved a street side with a naughty slippery wriggle which provides the users with variety in an essentially standardised programme, and helps to establish the building as a landmark: a visual fulcrum denoting where the old city's kernel meets the surrounding shell of inner urban nineteenth-century growth.

The two short end walls, east and west, are smooth and glossy. A special brick with dark green glaze has been made for them; they are only lightly pierced (at least in comparison to the long north and south sides), and seen straight on from the railway side, the west wail in particular has some of the fierce and mysterious glistening countenance of an ancient helm, especially because it is canted outwards towards the top, with the bricks being precisely laid with each course 10mm out from the lower one. This visor protects the building against the noise and pollution of the trains, and, like the more orthodoxly built and slightly more open countenance of the east end, it changes with the seasons and time of day, with hue and chroma continuously shimmering and fluctuating from deep black to almost the azure shine of the sky.

The green brick turns the corners onto the long sides of the building where it becomes a backdrop for the huge panels of glazing that are slightly proud of the glazed surface. I must confess to an instinctive dislike of this way of pushing the glass outwards and setting it in a sort of picture-frame - there are so many pompous and mediocre commercial buildings from the '60s which use the trick that I am prejudiced against it - particularly when it is to be seen raw and unadorned on the north side of this building. However, on the south side, the effect is greatly muted and made almost insignificant by a system of double brises-soleil which add a frilly frisson to the sexy wriggle. Above floats the thin aluminium-shiny aerofoil roof which simultaneously shelters the cafeteria and its terrace, orders the snaky plan geometry below and claims the building as a landmark.

The roof has a separate structure, propped on the concrete one below. In the latter, the main bearing members are 600mm deep precast concrete fins set at 1.625m centres, and concealed behind the brick and glass facades. Within the 600mm zone are the heating and wiring runs behind spandrels in the glass - the device is neat, but it must be difficult to achieve effective sound insulation between offices because of the large holes for services continuity cast into each fin.

The demand for cellular offices has often led to very dreary buildings with rows of cells ranged on both sides of dark internal corridors - unless of course site and budget allow for single-banked galleries. Here there could be no such spatial luxury, but the architects have ingeniously prevented dullness and monotony by inserting a wedge of vertical circulation and services into each end of the plan. This is what produces the external wiggle, and inside, it makes the branching corridors much more cheerful than those of a conventional bureaucratic building. Suddenly, one understands what the slits and slots in the north and south visors are for: they provide strips and spots of daylight which draw you towards the ends of the sinuous passages. Monotony is further combated by using two different kinds of artificial light, each on one side of the corridor only: a small but telling rejection of the 'economic' and conformist central lighting fittings so often found in such places.

The entrance to the offices is very understated, round the back in the north-east corner. It is easy to understand why German official buildings do not want to draw pompous attention to themselves, but this one seems to be going a bit too far the other way, verging on the secretive not surely a desirable trait in a building in which major decisions about people's minds are taken. Tucked under the main mass of offices, the entrance leads to a small hall, made more interesting by the void that shows the presence of a lower floor (it contains seminar rooms) and by the Mackintoshian treatment of the stair balustrades.

The public has to use this almost secret entrance when the top floor is devoted to private functions and so on. Up there, the great aluminium wing hovers over the cafeteria and much of its terrace, reflecting light down into the space and framing the view of the city to the south. All is transparent and open, in contrast to the sealed privacy of the offices below. It could be a pleasant place for a jazz concert, though the furnishing with rigorous rows of six person tables is not perhaps conducive to a festal atmosphere. Perhaps experience and use will modify arrangements.

There are certainly problems with the building, but they are far from serious. What matters is that architectural imagination has transformed a dull, prosaic programme into a noteworthy piece of city which contains a three-dimensional web of places in which users and (it is to be hoped) the public may find pleasure.