Go for a stroll by the water and breathe some fresh air at Marseille Fos Port. It's always relaxing watching the boats as they come and go.
When you've finished exploring this 2nd Arrondissement place for ships to anchor, why not make your way to Notre-Dame de la Garde, Chateau d'If, and La Vieille Charite? They're near Marseille Fos Port and also popular with tourists.