The burrowers.

A building designed to explain our most distant ancestors takes its place with grace and dignity in the ancient landscape of Aberdeenshire they helped to create.

Cullinan's have always had troglodytic tendencies: now they seem to be getting stronger. As long ago as the 1970s, the cooperative was using most unfashionable grass on the roofs of the Minster Lovell conference centre (AR April 1978), and more recently they drew an elegant carpet of landscape over the Readymix Concrete headquarters (AR September 1990). Apart from an atavistic desire to re-evoke one of our first habitations, the cave (which must surely be present, though it is never discussed), their underground work is driven by two principles: first, the need to make new buildings which relate to splendid old things yet have as little impact on them as possible;(1) and second (more recently) a concern to use the insulative and capacious qualities of earth to conserve energy.

So it was with a great deal of sensitivity for the ancient and the earth that they arrived in Aberdeenshire. Having been appointed as architects for the Stonehenge visitor centre following their triumph at Fountains Abbey (AR November 1992), they were clearly an obvious choice for the Archaeolink, set up to explain the prehistory of Aberdeenshire. This is the area that sticks out east from northern Scotland like a hunched shoulder. Cut off from the north by the Great Glen, the west by mountains and fringed by the sea, the county has always been rather remote, now no less than in prehistoric times, since when its rolling surface of forest and fields has been continuously and profitably farmed.

The undramatic landscape can be wonderfully beautiful. I was there in late autumn: a silhouette of snow powdered hills defined the north and west; low sun burnished bright yellow stubble and dark green woods under a deep blue sky, from which came the urgent Arctic cries of southbound skeins of geese. Glancing light revealed the gentle curves of the land and traces of humanity's continuous engagement with it. Shadows of standing stones told the time as they have been doing for 5000 years; defensive Pictish patterns of ditches and banks (merely two millennia old at most) were etched in shade. Behind that ridge Agricola's legions defeated the Caledonians at the battle of Mons Graupius; down there, eighteenth-century improvers rationalized agriculture by draining valleys and redefining boundaries to engrave the agrarian revolution's technological and social structures into the land.

We know what happened a couple of centuries ago because everything was written down. The Archaeolink centre exists to try to explain what happened before writing existed. You see it first on the left as you go up the wide Oyne valley towards the hamlet: a big conical grassed mound, clearly an artefact, but at the same time, part of nature. It evokes the simplicity of the works of the ancestors, but plainly, it is not theirs: it is too crisp and uneroded by time. The cone's relationship to the landscape is gradually revealed as you approach it. Immediately to the south, on axis with the entrance from the road down the valley is Berryhill, its top crowned by an Iron Age fort.(2) Above and beyond, the sharp outline of the Bennachie ridge (a mythic slumbering Celtic giant) emerges suddenly from the lowland to form a craggy skyline. So you walk south from the car park, aware of our homage to the past in the cone, then the ancient city on the hill, then the magic mountain behind it.

The cone's curve conducts you through a grassy cleft in the ground to the entrance, a glass plane which cuts straight across the little valley. You can see direct through the narrow shank of the building from entrance through a similar glass wall on the other side. The glazed space is ordered by round columns inside each glass wall and populated by four large coloured drums. Blue and green frame the entrance, left for the loos and right for reception. Further left is the largely carved-away red cylinder which signals the servery of the cafe, a rectangular continuation of the entrance hall that begins to burrow into the hillside to the south, where it terminates in a ceremonial fireplace. This is comforting and cheerful on a cold day,(3) but on hotter, sunnier ones the glass wall can be drawn back to allow the cafe to spill out onto the west terrace.

Had you turned right at the entrance, you would have been led to the inner mysteries through the bookshop which occupies most of the rest of the building's shank. Gradually, it becomes clear that the cone contains a dome surrounded by a circular ambulatory. The idea of magic cave within a ceremonial mound is very ancient, and everyone from Merlin to Lethaby would have welcomed it. This one is a very great disappointment. The central space contains an audiovisual display about the prehistory of the area which, had it been created 35 years ago, would have been hailed as a remarkable breakthrough. Now, if the technology does not actually creak, the storylines certainly do. But real distilled naffness is kept for the ambulatory, which is made into a series of plastic caverns punctuated by video screens, labels and dull dioramas. None of this tiresome triteness is of course by the architects, whose essentially chaste and dignified spaces could have been the setting of much finer and more informative displays which might have had some real resonance with the awesome nature of the works the place is supposed to explain. This is marketing, not curatorship. The vulgar marketeer's riposte to criticism is that he must provide what people want, yet surely here visitors are seeking inspiration and enlightenment rather than ersatz experience.

It is a relief to escape from the temple of kitsch and go out onto the west terrace and walk up the ramps that bring you to the flat roof over the shank. At the side of the cone, you turn round to find that the path you have just pursued is exactly on axis with the extraordinarily dramatic Dunnideer, an echoing conical hill on the horizon, crowned by a Pictish fort, on top of which is the picturesque silhouette of a ruined medieval castle. Then you go on up Berryhill, past recreations of Roman camp and Pictish farm (much more successful than the offerings in the mound because they are made of real materials with real craftsmanship), on up the steep slope through regenerating forest, on to the old fort at the bald top of the hill (now no more than a ditch and the remains of a stone wall).

From there, you look down on the relatively puny works of modern man. They are trim, dignified, elegant contributions to the landscape. But what you can't see is how much more ingenious we are than the ancestors in our homage to earth. Under the grass all round the building is a 4m wide skirt of insulation. Carefully waterproofed and protected from mechanical damage, the 100mm thick layer traps heat from floors and underground walls. The ground below the skirt will gradually warm up and become a heat reservoir to maintain the building above freezing even on the coldest days when artificial heating is turned off (the place closes in midwinter). It will be heated largely by solar energy through the glass walls. These have automatic external blind systems to prevent excessive glare and overheating, and on the hottest days, the glass walls will be opened to cool the whole place down. The systems are simple and direct, apt for a building devoted to explaining elemental forces and the history of humanity's relationship to them. P.D.

1 The story of their work on the visitor centre for Stonehenge is fraught with horror, combining the turgidity of the British planning system with the Herodian wildness of the Chairman of English Heritage.

2 Such forts, the first cities of the area, were on the hilltops, which were more easy to defend than lower ground, and could command the slopes where crops were grown. The valleys were wet and uncultifiable.

3 And, at the moment a bit kitsch, for someone has built a low random stone wall round the blaze, which was supposed to burn on a simple stab, The wall not only looks as if it has been stolen from a suburban garden but messes up the fire's draught system.