Place des Vosges is the rare Parisian square that’s genuinely walkable in August — the 17th-century arcade runs continuously around all four sides, and you can shop, eat, and wait out a midday sun without ever stepping into it. The Marais lanes radiating out (Rue des Rosiers, Rue Vieille du Temple, Rue Saint-Antoine) are narrow enough that the buildings on the south side throw deep shadow on the north sidewalk by noon.
These three keep you on the shaded side of each lane and route you onto the arcade whenever the path crosses it.