Centro Histórico in July

March through May gives you perfect weather without the summer crowds—think warm days and cool evenings ideal for rooftop drinks. September through November brings crisp air and clear skies that make the colonial architecture pop in photos. December gets packed with holiday celebrations, but the energy is infectious if you don't mind sharing the sidewalks. Skip July and August unless you enjoy sweltering humidity and afternoon downpours that turn cobblestones into slip hazards. Early mornings any time of year offer the best light for photography and the calmest streets for wandering.