Arnold Arboretum
Harvard rents these 281 acres from Boston for a dollar a year on a 1,000-year lease, and Olmsted laid out the paths. Some 16,000 plants grow here, including a katsura raised from Sapporo seed in the 1870s. Picnicking is banned except on Lilac Sunday each Mother's Day, when 400 lilacs on Bussey Hill Road hit peak bloom.