Best base radius (1.8 km, dark blue circle): centered near Les Halles / Châtelet, it holds 30 of the 50 spots within roughly a 20–25 minute walk. It covers the 1st (Louvre, Tuileries, Palais-Royal, Rue Montorgueil), 2nd (Opéra edge, Passage des Panoramas), 3rd and 4th (the Marais, Place des Vosges, Île de la Cité, Île Saint-Louis), 5th and 6th (Latin Quarter, Saint-Germain-des-Prés, Luxembourg) and the southern edge of the 9th and 10th (Galeries Lafayette, Canal Saint-Martin bakeries).
Second circle (1.5 km, light blue): centered near the Grand Palais, it picks up 8 western highlights: the Eiffel Tower, Trocadéro, Arc de Triomphe, Champs-Élysées, Ladurée, Les Invalides, Musée Rodin and Pont Alexandre III. Montmartre, Père Lachaise, the Catacombs, Saint-Ouen and Vincennes are best reached by metro.
Suggested areas to stay: 1) Le Marais (3rd/4th), charming, central and full of pastry shops; 2) Saint-Germain-des-Prés (6th), classic Left Bank cafés, quieter evenings; 3) Louvre / Palais-Royal (1st), the most central, with easy metro to the western circle.