Together, the Boston Public Garden and the Boston Common are the central green area of the city. Located where the Beacon Hill and Back Bay neighborhoods meet, these public parks are adjacent, but intersected by a busy thoroughfare. They have distinct personalities: Think of the Public Garden as Boston’s front yard, carefully maintained and showy, and the Boston Common as the backyard, where the kids run around and play pickup baseball. 
Bordered by Arlington, Boylston, Charles, and Beacon streets, the Public Garden is the prettiest park in Boston. Established in 1837, it was inspired by the gardens of Versailles. Today, its 24 acres are crisscrossed with walkways and formally arranged flowers, trees, and shrubs, as well as five fountains. The exquisite flowerbeds change regularly, complementing the perennial plantings. Note that there are no restrooms in here, although there are next door in the Common at its visitors center and Frog Pond.
At the western side of the Public Garden, poised at the Commonwealth Avenue entrance, is a dramatic equestrian statue of George Washington. With a backdrop of the city skyline, it creates one of the most picturesque tableaus in the city. The small body of water nearby is called the lagoon. It’s a triumph of optical illusion—viewed from above, it’s tiny, but from anywhere along the curving shore, it looks much more significant. It’s home to swans and numerous ducks, who waddle about and swim between the shore and a teeny island in the northern end of the waters. It’s crossed by a diminutive footbridge.
In keeping with the Victorian atmosphere of the Public Garden, simple pedal-powered vessels called Swan Boats ★★ (tel. 617/522-1966) provide leisurely 12- to 15-minute rides around the lagoon (employees do the pedaling) from mid-April through early September Tickets are $4 for adults, $2.50 for kids 2 to 15, and free for kids under 2. Boats operate daily 10am to 4pm in spring and 10am to 5pm in summer. 
Compared to the Boston Public Garden, the larger, rambling Boston Common has less charm. Still, it’s well used and has lots of foot traffic. At the northeastern end is the appealing Frog Pond, which is a spray pool for children in summer, a popular ice skating rink in winter, and a reflecting pool the rest of the year. Also here is a small carousel and a small playground.
Winding along the eastern edge of the city, roughly following the contours of the waterfront, the Rose Fitzgerald Kennedy Greenway is a new central green space for Boston. A raised highway dominated this part of Boston until 2008, but after the “Big Dig” public works project moved I-93 underground, this much-welcome walkway of connected parks filled in the scar that the highway left behind. The park is 1 1/2 miles long and includes, at its the northern end, an enchanting carousel (open year-round, subject to weather), fountains (including the family-friendly Rings Fountain with jet sprays to play in), the Trillian Garden beer-garden (corner of High Street and Atlantic Avenue; closed in winter), and sculptures, murals, and other engaging public artwork. Food trucks dot the cross streets. The Greenway concludes on its southern end near the central transport terminal South Station, at the city’s financial district.
Near the northern end of the Greenway, adjacent to Long Wharf at 110 Atlantic Ave., Christopher Columbus Park is another appealing green spot downtown. It includes a tot lot/jungle gym for smaller children, a fountain spray park, benches and lawn for lounging, a circular performance area that occasionally has musicians, and a dramatic central trellis draped with wisteria vines in warm weather and blue lights in winter. 
For many Bostonians, the Charles River Esplanade along the Boston side of the Charles River, is where we meet friends to go walking (or running, or biking, or skating). Its 64 car-free acres have green spaces for picnicking and paved paths for biking and running (paths on both sides of the river go all the way to Watertown, a suburb 8 1/2 miles northwest of Boston). The Hatch Shell amphitheater is here, an Art Deco confection with a grass lawn where concerts are held throughout the summer—including the July 4th spectacular with the Boston Pops. The narrow Storrow Lagoon within this park has postcard-pretty footbridges at either end and is surrounded by elaborate plantings and shady trees. The major entrance to the Esplanade is at the Charles/MGH T stop, although the park can be accessed by eight footbridges that cross over Storrow Drive, the highway that divides the city from the park and river.
Midway between the Seaport District and the dense residential streets of South Boston, the delightful Lawn on D Street, 420 D St. (tel. 877/393-3393) is an urban playground with a grassy lawn, food concessions, and occasional live music and festivals. Young adults throng here at night to chillax on huge glow-in-the-dark swings. The closest T is World Trade Center, and then it’s a 10-minute walk.
Farther afield, in the Jamaica Plain neighborhood, the Arnold Arboretum of Harvard University, 125 Arborway (tel. 617/524-1718), is a spectacular living museum of plant species from North America and Asia, and a natural retreat for locals and visitors. Paved and dirt trails weave in and out of towering conifers, hardy rhododendrons, and centenarian trees (100 years and older). In May, acres of lilacs come into bloom, and there’s an impeccable bonsai collection on view April through October. After a snowfall the woodsy hills quickly fill with snowshoe and cross-country ski tracks. Because it’s operated by Harvard University, there are ample opportunities to learn, including self-guided tours for kids or adults. The Hunnewell Building Visitor Center has a giant relief map and is wheelchair accessible, including the restrooms on the ground floor. It’s open daily from sunrise to sunset, and admission is free. To get here, take the Orange Line subway to Forest Hills and follow signs to the entrance.
And even further afield, a visit to one or more of the islands that make up the Boston Harbor Islands National and State Park lets you combine a ferry ride, a beach visit, nature walks, and fort-exploring all in one outing.

Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.