Jardim Botânico de São Paulo is a large botanical garden south of the centre, with lakes, glasshouses, native trees, and enough birdlife to make it feel calmer than most city parks. It sits near the zoo, so the two can work as a full green day away from central São Paulo.
The garden is best for a slow walk rather than a checklist visit. Come for shade, water, and Brazilian plant life, especially if you need a break from São Paulo's traffic and hard surfaces.