Musée de l'Orangerie audio guide,
five stops, free.

The room is an oval, and the paintings do not stop. They run round the curved wall, two metres high, with no frames and barely a gap between them, and the light falls on them from the ceiling rather than from any lamp. That was the point. Claude Monet designed this space himself, working with the architect Camille Lefèvre, and everything about it, the curve, the daylight, the empty floor, is there to give you what he called the illusion of an endless whole, of a wave without horizon and without shore.

There are eight compositions altogether, four in this room and four in the next, each two metres high and ninety-one metres from end to end. The two ovals sit one behind the other so that together they draw the symbol of infinity. They run east to west, in the path of the sun, along the same straight line that carries the Arc de Triomphe and the Louvre.

None of this was built for paintings. In 1852, at the request of Emperor Napoleon the Third, this was put up as a winter shelter for the orange trees of the Tuileries garden, which had until then been kept in the Grande Galerie of the Louvre. That is why the wall facing the Seine is glass, to catch the light and the heat, and the wall facing the rue de Rivoli has almost no windows, to keep out the north wind. For the next seventy years the building held orange trees, and also banquets, concerts, horticultural contests and dog shows.

Then came the war. On the twelfth of November 1918, the day after the Armistice, Monet gave the Nation his first two large panels as a symbol of peace. Georges Clemenceau, then head of the government, was the one who argued that the whole set should go here rather than into the courtyard of the brand new Musée Rodin. The donation was formalised in 1922, and Monet kept working. He was still working when he died in 1926, and he never saw the panels on these walls. Clemenceau opened the museum on the seventeenth of May 1927, a few months after the artist's death.

Now look closely at the surface. These are not canvases hung up in frames. The panels were glued directly onto the wall. The composition called The Clouds is three separate panels joined edge to edge, two metres high and twelve and three quarter metres wide, and if you stand near it you can find the seams.

The rooms have not always looked like this. Between 1960 and 1965 the museum built two floors inside the building to house the Walter-Guillaume collection, and a monumental staircase replaced the vestibule that led in here. The daylight went. It came back only with the renovation of 2000 to 2006, which pulled the floors out again and reopened the ceiling, which is why what you are standing in is both the oldest idea in the museum and one of its newest rooms.

In 1952 the painter André Masson called this ensemble the Sistine Chapel of Impressionism, and the phrase stuck. The museum asks you to look at it quietly, which is what Monet wanted. Give it a few minutes before you go down the stairs. The water keeps changing as your eyes adjust to the light.

He is sitting in a chair that is barely painted, against a wall that is half orange and half grey-green, and everything about him is slightly wrong. The neck is too thin for the head. One ear is enormous. His hands are folded over a white cloth on the table in front of him, with a smear of red running straight through them, and that red is the loudest thing in the room.

Chaïm Soutine painted this pastry cook in 1922 or 1923. He had been born at Smilovitchi, in what is now Belarus, in 1893, and in Paris he was not yet a name. The museum's own notice calls this subject the decisive moment in his career, and here is how that happened.

Paul Guillaume was out hunting for Modiglianis when a writer and critic called Michel Georges-Michel, who had published an article on Soutine, pointed him towards the painter. Guillaume bought one of the pastry cooks and later described it in his own review, Les Arts à Paris. An extraordinary, fascinating, real and truculent pastry cook, he wrote, afflicted with an immense and magnificent ear, surprising and just right. A masterpiece. So I bought it.

Then the American collector Barnes came to Paris, saw the picture at Guillaume's place and cried out, It's a peach. That one moment of spontaneous pleasure changed Soutine's fortunes. Overnight he went from unsellable to sought after by patrons, a painter to be taken seriously, a hero in Montparnasse.

The canvas Barnes carried home is not this one. It is in the Barnes Foundation in the United States. Soutine worked in series and painted six versions of the pastry cook that we know of, and Paul Guillaume bought this one in the early nineteen thirties, in memory of the first one, the one he had let go.

The pose may have come from a painting a few hundred metres from where you are standing. The museum's notice says the pose could have been inspired by Jean Fouquet's portrait of Charles the Seventh in the Musée du Louvre.

So look at the ear, and then at the jacket, which is not white at all but grey and green and pink in long nervous strokes, with the red cloth punched into the middle of it. Soutine signed at the lower right, in red, and the letters lean the way everything else in the picture leans.

Two girls at a piano. One is playing, sight-reading with her right hand; the other leans over her shoulder to follow the score. And behind them, nothing. No wallpaper, no furniture, no room, just loose strokes of blue and green and yellow that never resolve into anything. That absence is the clue to what this picture is.

In 1892 Renoir was asked, informally, for a painting for the Musée du Luxembourg. He worked the composition out over and over. The museum's notice here says at least six other versions exist. The one the State got hangs today in the Musée d'Orsay, across the river. Another, from the Robert Lehman collection, is at the Metropolitan Museum in New York. Two more are in private hands. And the one in front of you, a hundred and sixteen centimetres by eighty-one, is an oil sketch, with most of the background stripped out.

That is why people arrive at the Orangerie looking for the famous one and end up standing here slightly confused. This is not the famous one. It is arguably the better one to stand in front of, because you can watch him thinking.

Renoir loved music, like most of the Impressionists, and he came back to young women at a keyboard again and again. So did Cézanne, so did Manet, so did Degas. The subject goes back further than any of them, to the gatherings of musician painters in the seventeenth and eighteenth centuries. What Renoir does with it here is set the hard geometry of an upright piano against the curves of the two girls, and then refuse to add anything else.

It may well have been painted at home. He had bought his wife a piano as a wedding present in 1890, two years before this.

So look at the blue sash on the seated girl's white dress. It is the one saturated colour in the bottom half of the canvas and it holds the whole thing down. Then look at the pink sleeve of the girl leaning over her, resting against her friend's loose blonde hair. And then find the signature at the lower right, in dark red, a single word, Renoir, which he put on a sketch as confidently as on anything he finished.