House of shadows.

Tadao Ando's recently completed museum for the study of ancient Japanese burial mounds has both formal rigour and spiritual intensity.

The southern part of Osaka prefecture contains a remarkable aggregation of ancient Japanese burial mounds (kofun), dating from the fifth and sixth century. Scattered across the undulating terrain are about 200 tumuli, among them four imperial tombs with characteristic keyhole forms and the tomb of Ono-no-Imoko, Japan's first ambassador to China. The new Chikatsu-Asuka Historical Museum was conceived as a centre for exhibiting and researching kofun culture.

Tadao Ando has sought to create a building that transcends the scope of the conventional museum and act as a focus for both excavated objects and adjacent clusters of tumuli. These remain largely undisturbed in their original settings. In many respects, Chikatsu-Asuka has much in common with the Forest of Tombs Museum in Kumamoto (AR April 1993). At Kumamoto, the strong sculptural form of the building acted almost as an organic extension to the landscape, providing an elevated vantage point from which to view the surrounding tombs (with minimal disruption to the site) and also functioning as a repository for exhumed relics.

A similar proposition informs the new museum. The area is relatively remote and as visitors stroll through the tranquil countryside they encounter an unexpected man-made form in the recess of a valley. Like a Mayan temple emerging from the deepest jungle, the building has a brooding, monolithic presence. The roof of the structure is, in effect, a monumental staircase leading to a broad open-air terrace. From this exalted position, visitors can survey the burial mounds and surrounding landscape of hills, plum trees and a small lake. The immense tiered plateau is also intended as a forum for outdoor activities of many kinds - drama and musical performances, lectures and festivals, encouraging the museum's active participation in the cultural life of the region.

The entrance to the complex below is cryptically indicated by a long path incised at an angle into the staircase, like a sharp wound in the flank of some slumbering behemoth. The oppressively narrow route appears to lead nowhere, but in fact emerges adjacent to the projecting cube of the entrance. From the brilliantly skylit entrance hall, there is a slow and symbolic descent into metaphorical and literal darkness. The sequence begins with the museum's permanent collection on the entrance level and extends around a wide balcony, which overlooks a display area below. The strange keyhole form of the lower level evokes the distinctive shape of the tumuli and is dominated by a vast and intricate model of a burial complex.

Around the sides are dimly lit cases of artefacts, inducing an atmosphere of calm communion and sepulchral claustrophobia. Descent to the lower level is by means of a curving ramp at the round end of the 'keyhole form. The museological circuit extends beyond the keyhole to a quadrant-shaped temporary exhibition space; beyond this is a foyer leading to a compact auditorium.

As with all of Ando's buildings, formal and spatial concepts are executed with a rigorous but poetic intensity. Here he further explores the notion of an architecture that can initiate and marshal an extreme range of experiences - from breathtaking survey of the landscape to intimate contemplation of precious historical relics. By developing the stage set possibilities inherent in the Kumamoto Museum, Ando has fused together a sequence of spaces and events that constitute more than a simple museum visit - instead it becomes a mystical progress concerned with the essential nature of man and his place in the world.