Solid and void: a small museum for the works of one of the most important sculptors of this century constitutes a moments of contemplative peace in the busiest public square in Paris.

A small museum for the works of one of the most important sculptors of this century constitutes a moment of contemplative peace in the busiest public square in Paris.

Modest though it was, the studio space lit by cool north light acquired singular importance for Brancusi. He came to see his works and the spaces around them as a single harmonious entity. He placed completed and uncompleted sculptures singly or in groups (groupes mobiles) so that their relationship one to another and to the containing room was in balance. In his search for unity, he continually made adjustments, putting some sculptures on turntables to see how the entity could be changed and made afresh. In the end, it became difficult for him to envisage the sculptures outside the studio and by 1950 Brancusi refused to exhibit his work elsewhere. The year before his death, he left the studio and its contents, including sketches, tools, books and records, to the State with the request that it should be left undisturbed.

Soon after Brancusi's death, the studio was demolished; nearly 20 years later, a replica was built opposite the north-west corner of the Centre Pompidou on the outer edge of the Piazza, where the Rue St Martin meets Rue Rambuteau. Faithful to the picturesque scruffiness of the original, it was a quietly poignant place, the more so for being next to the frenetic glamour of the Centre Pompidou's Piazza. The little building was difficult to make secure, and in consequence hardly advertised and open only two afternoons a week.

Renzo Plano's scheme for renovating the Centre Pompidou included building a new Atelier Brancusi on the same site. Now completed, the scheme is an evocation of Brancusi's spirit rather than another replica. At the same time, the building conforms to standards required by modern curators, and accommodates a limited number of visitors.

From the Piazza, you scarcely notice Plano's quiet stone pavilion, which spans a change in level up to Rue Rambuteau. There is just a plain wall of stone blocks with the long low metallic pitch of a shed roof above. Mounting the steps to one side, you descend to your left to a discreet glazed entrance, between another plain wall on the street side and a small courtyard planted with trees on the other. Because the building is set below street level, it feels separate from it, and the descent forms a gradual transition from street life to the contemplative place you find inside.

Brancusi's studio at the centre of the building echoes the original in plan and section. It consists of a wooden-framed structure divided into four interconnecting spaces with plain white walls lit by north-facing skylights. The studio is isolated from human contact by glass walls and visitors circumnavigate in an ambulatory that runs round the perimeter. Inside, the sculptures - and various touching objects like Brancusi's worn tools - are arranged presumably as he would have wished. It is a pity though that the studio is isolated. It may be necessary for security reasons, but seeing the studio through thick glass walls - as well as the absence of anything to sit on - impedes the contemplation the architects want to promote.

The ambulatory widens on the north-west side into a small gallery for Brancusi's photographs. Here, at each end of the axis running parallel to the street, windows cut into the walls remind you that the material as well as the spiritual world exists, though the level and the absence of noise renders it unreal.

The components of the interior are few and austere: the plain stone of the four enclosing walls and simple white planes of inner ones; underfoot is polished grey concrete. The light is cool and beautiful. North light shed over the sculptures in the studio is enhanced by daylight filtering through white fabric panels that form the ambulatory's ceiling and entering through the glazed facade from the shady courtyard.

This is an immensely civilised building for an emotional and spiritual legacy of great importance. Piano's treatment of what must have been a thorny problem is both inspired and dignified. The poignancy of the original is there, and in spite of the cool ascetism of the building, a degree of intimacy is conveyed.