In addition to the connection with Thoreau, Walden Pond State Reservation  (915 Walden St., Concord, 978/369-3254, www.mass.gov ) draws hordes of summer visitors every year to swim in its deep, cool waters. Be forewarned that the only parking available is in the official lot, which fills up quickly on hot summer mornings.
Situated along the banks of the Concord  and Sudbury Rivers, the Great Meadows National Wildlife Refuge (73 Weir Hill Rd., Sudbury, 978/443-4661, www.fws.gov/northeast/greatmeadows ) contains almost 4,000 acres of meadow and marshland that teems with wildlife. Trails wind their way through both parts of the reservation, one located in Concord and the other in Sudbury. Among the wildlife that can be spotted are deer, red fox, and great blue herons.
Before Walden, Thoreau wrote A Week on the Concord and Merrimack Rivers. You can follow in his paddle marks by renting a canoe at the South Bridge Boathouse (496 Main St., Concord, 978/369-9438, www.canoeconcord.com ) for a trip down the heather-lined banks of the Concord River.