Along with the artists of Montmartre, the Eiffel Tower and Notre Dame, one of the most enduring images of Paris is the cafe-dwelling, black- clad existentialist, smoking Gauloises and offering up the occasional bon mot. But there's more to Paris and philosophy than existentialism and some over-priced cafes. If you're planning a trip to Paris and want to find out more, set aside a few hours for a walk along the philosophers' Rive Gauche.

Begin at place Saint Germain-des-Pres, easily reached by the Metro station of the same name. This square lies on boulevard Saint-Germain, whose cafes were once the prime meeting-places of philosophers and intellectuals, but which now, sadly, is more renowned for its traffic and tourists. On the north-east side of the square lies Les Deux Magots, possibly the most famous cafe in Paris, and one-time favourite haunt of the French intelligentsia. The cafe's reputation is a little misleading, however, for existentialists such as Jean-Paul Sartre (1905-1980) and Simone de Beauvoir (1908-1986) in fact preferred to take their caffeine next door, at the Cafe de Flore. And far from being idle chatterers, philosophy's glamour couple sat at separate tables, diligently writing their influential works. Philosophy of sorts still happens here during the monthly English-language cafe- philosophique, where anyone can walk in and take part in a philosophical discussion.

Given the prices, this is perhaps not the best place for a rest, so cross over the square to Paris's oldest church, Saint Germain-des-Pres, which dates back to 542, though most of its features, including the tower, were added in the 12th century. It contains the tomb of Rene Descartes (1596- 1650), arguably the most important figure in modern western philosophy. The interior of the church is relentlessly gloomy, and the monument to Descartes surprisingly modest.

Opposite the church, walk along rue Bonaparte for a few minutes until you get to place Saint-Sulpice. Here you will find Visconti's fountain and, more pertinently, the Cafe de la Mairie. Sartre and Albert Camus (1913-60) met here for the last time in 1951. Having worked together on the radical left-wing newspaper Combat, the two fell out, never to meet again. The cafe was also a favourite meeting-place for Paris's many literary emigres, such as Hemingway, Fitzgerald and Beckett.

Walk around to the back of the church that lends its name to the square and then turn left down rue de Seine, crossing boulevard Saint- Germain, until you come to another cafe, La Palette. A haunt of students from the Beaux Arts school since the beginning of the century, this was another favourite of Sartre and de Beauvoir. Set on a reasonably quiet cross-roads, this is one of the better of the historical cafes to stop off at, especially if you get one of the outside tables. Any cafe you stop at is going to be pricey, and this is about as atmospheric as you're going to get on the modern-day Left Bank.

Continue along rue Callot and then turn back towards boulevard Saint- Germain along rue de l'Ancienne-Comedie. Here you'll find Paris' oldest cafe, La Procope, which first opened in 1686. This became a focal point for many in the French enlightenment, foremost among them Denis Diderot (1713-84). Influenced by the English empiricist John Locke, Diderot's radical ideas foreshadowed much later theories such as evolution and eliminative materialism, and it was here at La Procope that Diderot and D'Alembert first conceived the Encyclopedie, a landmark in scholarship but also a challenge to the authority of the Catholic church.

Rejoining the boulevard Saint-Germain, continue along, before branching off to the right along the rue Ecole de Mede, turning into the rue des Ecoles. Apart from the gloriously tacky Boutique Descartes, you will come to the Sorbonne, one of Europe's oldest and most distinguished universities, where Sartre and de Beauvoir were both students.

Turn right on to the rue Saint- Jacques and continue up until you come to the rue Soufflot. At the end of this road stands the imposing sight of the Pantheon. Originally commissioned as a church, on its completion in 1790 it was turned into a shrine for France's great and good by the Revolutionary Assembly. The crypt contains the remains of the political philosopher, author of The Social Contract and guiding light of the French Revolution, Jean-Jacques Rousseau (1712-78). A statue of Rousseau also stands, incongruously, in the car park outside, as ignoble a site to remember him as the Pantheon itself is impressive. Others buried here include Voltaire and Zola.

Walk away from the Pantheon, to the right, until you get to rue de l'Estrapada. Follow this along to the left for a few minutes and you will arrive at the place de la Contrescarpe. This delightful square, with a calming central fountain, is quieter than a lot of the more central locations and provides the ideal spot to sit around and soak up the atmosphere.

You may wish to end your tour here, but one sight remains which the dedicated philosophy pilgrim would not want to leave out: the joint grave of Sartre and de Beauvoir. Hop on the Metro and make your way to Raspail station, or you can walk via the green and pleasant Jardin du Luxembourg. Tracing your steps back to the Pantheon, follow the rue Soufflot to the boulevard Saint- Michel. Turn left along this road for about 500 yards until you see the entrance to the Jardin on your right. When you leave the Jardin at the opposite end from the Palais, follow the narrow green stretch of avenue de l'Observatoire. When it turns to road, carry along and then turn right along the impressive boulevard du Montparnasse.

A left turn along rue Huygens at the junction with boulevard Raspail will take you to the entrance of the cemetery, where a free map is available at the warden's lodge. To find Sartre and de Beauvoir's modest gravestone, just turn right inside the gates, and you will find it barely half-a-dozen graves along.

The walk starts at Metro St-Germain-des-Pres (line 13) and should take between two hours and a whole day depending on how long you stop off along the way and whether you decide to walk to the Cimitiere Montparnasse.