The conservation movement started here, in a small wooden structure where a misunderstood social activist moved to "live deliberately." A pile of stones marks the site of the cabin where Henry David Thoreau lived from 1845 to 1847; he captured the experience in the book Walden. Today the picturesque park is an extremely popular destination for walking (a path circles the pond), swimming, and fishing. Although crowded, the park's 462 acres are well preserved and insulated from development, making it less difficult than you might expect to imagine Thoreau's experience. Check ahead for the schedule of ranger-led interpretive programs. No dogs or bikes are allowed. In good weather, the parking lot fills early every day -- call before setting out, because the rangers turn away visitors after the park reaches capacity (1,000).