"So Sid," I hear you say, "We like the city, but enough with the concrete and asphalt. My soul cries for more grass and trees while my feng shui advisor insists on more water. What can we do?"
Fear not. Sid comes through for you!
Walk down to the Boston Harbor Cruises ticket booth on Long Wharf and buy a ticket ($10, $7 for children under 12, $25 family rate for two adults and two children) to George's Island. Forty-five minutes after boarding you've watched the city recede behind you, cruised around ships and sailboats, threaded between islands and are disembarking at George's Island, the central point of the Boston Harbor Islands national park area.
Stay here awhile and explore Fort Warren, an 1850 fort for the defense of Boston Harbor used as a prison for captured Confederates during the Civil War. Rangers give tours throughout the day, but you can walk around on your own, too. Bring a flashlight if you really plan to explore. There's a snack bar, but avoid it. Plan ahead and pack a lunch - buy only cold drinks here. Be aware: This is the only snack bar on any of the islands. Also - there is no fresh water on any island. Make sure you bring drinking water.
Next take a free shuttle to explore one of the other park area islands. All have rangers, trails and abandoned military structures being absorbed by nature. Take a look at the shuttle timetables and pick an island based on how well the shuttles fit your schedule. Each island has its own character. Most people simply visit George's; if your time is limited, that's fine, but you should hop to one of the quieter, less visited islands if possible.
Swimming is limited, and is restricted on some islands, but it's a non-issue. The water's clean but cold. Stick your feet in the water for more than two minutes and feel your ankles start to go numb. Visitors from Hudson's Bay may consider the water warm enough for swimming. The rest of us simply walk in a bit to cool off.
During the summer, boats leave Boston every hour on the hour from 10 am to 5 pm. One more warning: if you must do this on a Saturday or Sunday, get to the ticket booth well before the first boat leaves. By mid-day on a weekend your wait in line to buy a ticket may be longer than the cruise to George's Island!