It is less than 15 miles from the Boston Public Garden to the colonial town of Lexington, a brief journey that takes you from the bustling heart of the city to a tranquil setting of green spaces, white steeples and clapboard houses. Although not at the geographical center of New England, Lexington is its spiritual heartland. Of course, this is famously where the first shots were fired in the Revolutionary War. Visitors come to take a historical tour of Battle Green, wander around the Minute Man National Historical Park and ride along the 11-mile Minuteman Bikeway. Just 6 miles to the west, on the outskirts of Concord, are houses that once belonged to Ralph Waldo Emerson, Nathaniel Hawthorne and Louisa May Alcott. And a mile or so farther on is Walden Pond, where Henry David Thoreau lived in a cabin for two years, on land owned by Emerson, a sojourn that provided the material and the impetus for his book “Walden; or, Life in the Woods.”