I recommend arriving by public transport and parking your car in one of the P+R car parks around the city. Alternatively, you can park in one of the many Semepa car parks around the city centre.
PS: Both options are paid, but the P+R is much more affordable.
Start from Parc Vendôme, via the Rue de la Molle entrance (bus station).
(S/E) Enter the park, first turn right then left and cross the park. Turn left then right to exit onto Rue Celony. Follow this street to the left. Cross Cours Sextius, go to the fountain and turn around to take Avenue des Cordeliers.
At the end, turn left twice. Immediately turn left onto Rue de la Treille. Takethe first right onto Rue des Muletiers. At the end, cross Place des Cardeurs to reach Fontaine Amado.
(1) Then turn left and go up Rue Venel. At the end, turn right twice to follow Rue de l'École. Takethe second left, Rue du Plan. At the end of this short street, go up Rue Gaston de Saporta on the left to reach Saint-Sauveur Cathedral. Continue along the street to the next crossroads.
(2) Continue straight ahead on Avenue Pasteur and, after about 50 metres, turn right and walk past the monument in honour of Joseph Sec. Turn right again into a courtyard. Retrace your steps, cross Boulevard Aristide Briand and you will arrive at the previous crossroads.
(2) Turn left onto Rue des Menudières. At the end, turn right onto Rue Pierre et Marie Curie. Take the first left onto Rue Loubet. When you reach Place Jean Richard, turn left onto the Bellegarde car park pedestrian crossing. Join Boulevard Aristide Briand and follow it to the right to reach the Bellegarde Fountain.
Then turn right towards the historic centre. Follow Rue Mignet and pass the Puits Neuf fountain. At the Deux Canons fountain, turn right onto Rue Boulegon. Continue straight ahead until you reach the next fountain and cross Rue de Matheron.
(3) Turn left onto Rue Loubon. At the end, turn left onto Rue Jaubert, cross Rue Matheron again, then Place des Trois Ormeaux. Then turn left onto Rue des Épineaux. At the end, turn right onto Rue Constantin. At the end, turn right again onto Rue Mignet (gateway to the Ursuline Chapel). Walk down the street to reach Place des Prêcheurs.
Go around the right side of the Madeleine Church and take Rue Portalis. Cross Rue Chastel and go to Place Joachim Gasquet (Fontaine Saint-Louis on the other side of the boulevard of the same name). Then take the first right, Rue de Lacépède. Before the Sacré Cœur church, turn left onto Rue des Bretons. At the end, take a passage on the right and then a staircase. Follow Rue Manuel to the left. Continue to Place Miollis (fountain).
(4) Turn right onto Rue de l'Opéra. Further on, take the first right, then immediately left onto Rue de la Mule Noire. At the end, continue straight ahead onto Rue Ganay. Turn onto Rue Emeric David and follow it to the left to reach Place de Verdun.
Turn left opposite the Palais de Justice and cross the square. Continue along Passage Agard, which leads directly to the top of Cours Mirabeau. First turn left then right and cross Place Forbin.
(5) Turn right onto Rue d'Italie. Take the second right, Rue Cardinale, which leads to Place de l'Église Saint-Jean-de-Malte, where the Granet Museum is located. Continue along Rue Cardinale, go straight ahead and pass the Fontaine des Quatre Dauphins fountain. Take the next right, Rue Joseph Cabassol.
Turn right at the first street, Rue Goyrand. Pass the Three Tritons Fountain and cross Rue du Quatre Septembre. Then turn left onto Rue Frédéric Mistral. Turn left onto Rue Mazarine, then right onto Rue du Quatre Septembre. You will arrive opposite the Moussue Fountain on Cours Mirabeau.
(6) Walk down Cours Mirabeau on the left. At the next fountain, turn right onto Rue Nazareth. At the end, turn right onto Rue Espariat. Pass Place d'Albertas (fountain). Then take the first left, Rue des Bagniers. Turn right onto Rue des Chapeliers, then left to arrive at the foot of the Court of Appeal.
Turn left onto Rue Monclar. Turn left onto Rue des Chaudronniers, then continue along Rue Laurent Fauchier. Take the first right to reach Place Riquelme. Cross the square diagonally to the right, then turn left onto Rue Vauvenargues to reach Place de l'Hôtel de Ville.
(7) After going around the square, go down Rue du Maréchal Foch. Return to Place Riquelme and turn right onto Rue des Marseillais. Turn left onto Rue de la Verrerie. At the end, turn right onto Rue Felibre Gaut, then immediately left onto Rue de l'Annonciade. Continue straight ahead until you reach Place des Tanneurs.
Cross the square diagonally to the right, then turn left onto Rue Fermée. At the end, follow Rue Lisse des Cordeliers to the left until you reach Place Paul Ferréol. Turn left onto Rue Victor Leydet. Take the first left, Rue de la Fontaine, then the first right, Rue des Bernardines. Cross Rue de la Couronne then turn right onto Rue des Tanneurs. At the end, turn right onto Rue Espariat.
Continue straight ahead to Place de la Rotonde (fountain symbolising the city).
(8) Go around the square on the left to reach Espace Cézanne, an iconic figure in the Aix region (S/E).

), but it's a good guide for visiting this city.