The Emerald Necklace at the Hour the Herons Fish

Frederick Law Olmsted's Emerald Necklace is a chain of nine parks that runs from Boston Common to Franklin Park, seven miles of connected green space that Olmsted designed in the 1880s to give the city a continuous nature walk that could be accomplished without ever crossing a major road. It's his masterpiece, and walking it end to end is the best way to understand both Olmsted's genius and Boston's peculiar insistence on being a walking city in a country that chose cars.

I start at the Back Bay Fens — a salt marsh that Olmsted restored from a polluted tidal flat — where the community garden plots bloom in chaotic proficiency and the reeds along the Muddy River hold red-winged blackbirds whose calls sound like rusty gates opening. The path follows the river south through Olmsted Park and Jamaica Pond, where the water is deep enough for sailing and the shore is lined with beeches and oaks that Olmsted planted specifically because he knew what they'd look like in 140 years. He was right.

Arnold Arboretum is the chain's jewel — 281 acres of labeled trees from around the world, arranged on rolling hills with the precision of a botanical garden and the beauty of a wild forest. In May, the lilac collection blooms in 400 varieties, and on Lilac Sunday the entire city seems to converge on the Arboretum with picnic blankets and the shared understanding that this particular combination of fragrance and color happens once a year and is not optional.

Best season: May for the lilacs, October for the foliage, any morning for the herons. The full walk is 7 miles; pick a section if time is short. The Arboretum alone justifies two hours. Bring comfortable shoes, water, and the willingness to believe that a man who died in 1903 designed something that is still making a city better.