Good buy: Le Corbusier apartment, Marseille

This sixth-floor two-bedroom duplex is situated within Le Corbusier's seminal Unité d'Habitation development in southern Marseilles. The building, also dubbed "the city in the sky", was a revolutionary experiment in urban living when it was built between 1947 and 1952.

Le Corbusier designed a string of Unités d'Habitation across Europe at around this period, but this one was the prototype and became the most famous example of the architect's brutalist style. He described it as designed "to make people think and to make beauty by contrast by establishing a play between crudity and finesse, between the dull and the intense, between precision and accident".

Making a virtue of necessity in post-war France, where steel was a scarcity, Le Corbusier pioneered the use of moulded cement. The result is fascinating in many ways, not least the way that the economies of building vertically are justified by the parkland setting. Also intriguing is the way that light is used and the creation of flowing open spaces around the base.

It was an ambitious project, with 337 apartments for around 1,600 residents spread across its nine floors. It deserves to be called a city, boasting its own shopping mall, hotel and restaurant, and on its roof terrace there is a school and recreational facilities including a swimming pool.

It is ingeniously designed internally, too. Each of its different levels, referred to by residents as "streets", in fact occupies two levels by virtue of the fact that the apartments interlock, so that those leading off from one side of its central gangways are entered at their lower level before ascending up to a double-aspect floor, while those on the other side open into single-aspect upper levels before descending to double-aspect lower levels.

This means that all of the apartments span the entire width of the building and enjoy double-height reception rooms on one level, and suites of long narrow bedrooms on the other level. It also means that they are well soundproofed and that the entrance corridors leading off from the main service shaft are only required at every third level.

The layout of this particular flat is with front-door access to its lower level. Its current owner, a museum curator called Françoise Guichon, bought the duplex about 10 years ago. She says that she is a great fan of the building's style and ambience, and that, in this respect, she is fairly typical of the building's other residents. "The people living here have deliberately chosen to live here," she says. "They love and respect the place."

Françoise's front door opens on to a parquet-floored double-height reception area, with a kitchenette to one side and a balcony at the far end looking eastwards over the hills. A stylish staircase ascends from here to a bedroom with an adjoining shower room and a west-facing balcony with sea views, while an east-facing mezzanine bedroom and bathroom are tucked away on the other side of the landing.

The ingenious use of space and light is as much a hallmark of the building's internal design as of its exterior. "It has been a real architectural experience living here," says Françoise. "Because the building faces both east and west, and because the flat's two levels are opened up and double-height, there is always a complex interplay going on between the space and the light. It changes every minute, every second of the day, and is endlessly fascinating."

Françoise is especially proud of the excellent condition of her apartment. The upper-level master bedroom was, at some point, created by knocking through two narrow bedrooms that used to occupy the space. However, other than this, the apartment's structural layout has not altered since it was first put together back in the 1950s.

"It's a bit like a museum," says Françoise, drawing particular attention to the lovingly preserved original Charlotte Perriand-designed kitchen as well as the distinctive modernist staircase designed by Jean Prouvé, another of Le Corbusier's close collaborators.

For Françoise, the latter feature is "a mini masterpiece", in the design of which she detects a nautical inspiration, a theme echoed in the cabin-style bathroom on the upper level. The period feel of the flat has been enhanced still further by Françoise's judicious choice of artefacts and furniture to blend in with its prevailing style, such as the set of tables and chairs that is also the work of Jean Prouvé.

After more than 20 years of living in Marseilles, Françoise has decided that it's time to move on and has accepted a new curating job in Paris. She fears that she will really miss her old apartment, and expects that whoever ends up buying it will be fellow Le Corbusier enthusiasts.

"The Unité d'Habitation is still a very vibrant place with a great atmosphere, even though it is more than 50 years since it was built," she says. "There's an incredible mix of people living here of all nationalities and from all walks of life, but somehow the building manages to bring them together under one roof and to create a great community feel.

"You really have to hand it to Le Corbusier - he set out to create a city in the sky, and he succeeded."

Get the spec

What's for sale: A two-bedroom duplex apartment on the sixth floor in Le Corbusier's Unité d'Habitation in Marseilles.

Serious kit: Original kitchen by Charlotte Perriand and staircase by Jean Prouvé; a double-height reception room.

Extras: Stunning views over hills to east and the sea to west; shops halfway up the building; school and recreational facilities on the roof terrace.

How big? Gross internal area around 1,055 square feet, with two balconies.

Buy it: Through The Modern House (01420 520805; www.themodernhouse.co.uk), for €420,000.