Planet Niemeyer.

Poised like a spaceship on the edge of a cliff, Oscar Niemeyer's extraordinary art museum forms a seductive new landmark for the Rio suburb of Niteroi.

The extraordinary topography of Rio de Janeiro has a distinctly otherworldly quality. The city wraps itself around a sinuous, sensuous coastline of mountains and bays, where the manmade is overwhelmed by the immemorial presence of nature. On the east side of Guanabara Bay lies the dormitory suburb of Niteroi, linked to the city by a long bridge that traverses the mouth of the bay. Niteroi forms the setting for the city's new Museum of Contemporary Art, built to house the paintings and sculptures of one of Brazil's foremost modern art collectors. Formerly spread across the city in various locations, the collection is now unified in a single remarkable building designed by Oscar Niemeyer.

The new museum occupies a rocky promontory with breathtaking views towards Rio and the familiar hump of the Pao de Acucar. Given the alien quality of Rio's landscape, it seems appropriate that the form of the museum should most obviously suggest a flying saucer, seemingly poised for take-off on the edge of the water. Cantilevered out from a stout central stalk, the saucer-like volume of the building has an unmistakable iconic presence, its seductive, sci-fi geometry creating a new landmark for the district. Working to a relatively modest brief, Niemeyer re-investigates the organic form-making that characterized his early career (the Niteroi saucer, for instance, recalls an unbuilt museum project for Caracas executed in the early 1950s) and the technical demands that this makes on both structure and materials.

The building's concrete structure consists of three circular floor plates with radii ranging from 18 to 20m. These are supported by a central cylinder 9m in diameter. A serpentine ramp (rendered a coruscating Barraganesque pink) coils up languidly from the surrounding plaza to dock into the side of the saucer. The elegant interplay of curves is reflected by a circular pool at ground level. Painted a gleaming white, the untreated concrete structure embodies the evocative, monumental quality of Niemeyer's initial sketches. The building's sole articulation is a broad strip of glazing that wraps around its entire circumference like a visor. Black vertical mullions form a crisp contrast against the white carapace, magnifying scale and underscoring the building's function as a civic landmark.

The museum saucer is divided into three levels, with a separate subsidiary floor partly sunk below the plaza. Arranged around the base of the structural stalk, this lowest subterranean floor houses a screening room, archives, technical facilities and storage. Space has also been allocated for a proposed bar and restaurant, with views across the bay. Staff and administration facilities are housed in the lowest level of the saucer. The two upper levels are given over to gallery space; the top floor is devoted to installations and temporary displays and the intermediate level houses the permanent collection. Niemeyer neatly overcomes the 'Guggenheim dilemma' (the patent unsuitability of curved walls for the display of art) by creating an inner hexagonal-shaped core of space enclosed by flat screen walls. This generates surprising flexibility, although the stunning panoramas of Rio (visible through gaps in the screen walls and in the outer perimeter zone of gallery space) occasionally upstage the art.

Since its inauguration, the building has attracted great attention, enticing a regular stream of visitors across the bay to Niteroi. Yet the museum is only the first part of a more ambitious urban redevelopment plan to revive the suburb's fortunes. Niemeyer is currently evolving proposals for a new Catholic cathedral, a conference hall, offices and a municipal history and records centre, all of which aim to build on the cultural and architectural achievement of the musuem.