The embassy's location couldn't be more Dutch. It stands on the Rolandufer overlooking the River Spree - the Berlin equivalent to the Amstel waterway in Amsterdam - next to a sluice complex similar to the one beside the Carré Theatre in Amsterdam. Pleasure boats and freight vessels glide by constantly in the summer. This corner of the Mitte district in what was East Berlin feels out of the centre, but that's not the case. The embassy is built directly above the U2 tunnel, an important underground subway connecting west and east Berlin, and is just a stone's throw from the Ministry of Foreign Affairs.

Koolhaas has responded intelligently to Berlin's stringent urban-design regulations. Those regulations determine the perimeter massing by specifying development at each corner of the building site. But they do not specify what happens in between. And here the architect makes the most of this opportunity. The embassy takes the form of a free-standing cube at one corner of the site. Arranged around it is an L-shaped residential block, containing three dwellings for embassy staff, which defines the other corners.

Not much of the building can be seen at the moment because of the plastic covering that shields construction work, but the embassy immediately starts to reveal its story once you've penetrated the site. The most important organisational and structural device is the 'promenade' that spirals through the whole building. Each embassy department occupies a branch of this promenade, totally different in form to other branches. The promenade also forms a stable core that supports all floors. A source of despair for the German builders is the lack of any clearly recognisable levels, a direct consequence of the spiral form. Your first impression is of an exciting maze, with the promise of surprise around every corner. The route weaves its way through the cube, offering new and unexpected views of the building and, in particular, the city. Most spectacular of all (though still blocked by the plastic) is the diagonal view through the embassy and through an opening punched in the enclosing residential block. Framed in the opening is the Fernsehturm. This TV tower at Alexanderplatz, higher than it is beautiful, is an essential reference point for the entire city and soon, too, for the embassy.

Materials used are shiny metal, glass, concrete and dark timbers. Aluminium dominates along the promenade, wood in the offices. Even in this phase of construction it is striking how specific the architecture is. All 400 doors, for example, are different and made to measure. They range from a heavy 'front door' of natural stone to a James Bond door that disappears completely into a wall.

In line with how the embassy is run, each department has its own 'neighbourhood'. Flexibility would certainly not seem to have been high on the list of client demands, and you can only hope that renovation won't be needed to adapt the structure to changing requirements.

Embassy staff view the eighteen-month delay in construction of the 35-million-euro complex as just one of the hazards of the job. The thinking is that though the job may take time, it'll be worth it when finished. Obviously, in what is its most important embassy, the Netherlands is keen to present the image of a unique country. And unique the building certainly is. Wim Henskens, project manager of the embassy, don't mince his words: 'This is going to be the most striking building in Berlin!'