Ryan Smith A day-hiker has a serene stretch of the Bay Circuit Trail circling Walden Pond all to herself.

A furry head skims the surface of the pond a few feet from the trail. Then it’s gone, just a ripple and a question remaining: Was it a beaver? A river otter? I’m eager to get another look.

I’m only 100 yards into my weekend run, following the Dike Trail through Great Meadows National Wildlife Refuge in Concord, Mass., and already I’m captivated by the activity around me. Geese and ducks float and feed. Red-winged blackbirds cling to cattails, singing back and forth. At the trailhead, a chalkboard lists the day’s sightings: mergansers, buffleheads, wood ducks, a bald eagle. Someone has even scribbled a wishful “unicorn” at the bottom of the list. That might be pushing it, but there’s plenty of magic to discover along the Bay Circuit Trail (BCT).

On its 231-mile arc around Greater Boston, the BCT links dozens of parks, forests, and preserves—Great Meadows included—from the salt marshes of Newburyport on the north to the shore of Kingston Bay on the south. Conceived in the 1920s as a means of curtailing suburban sprawl and pieced together over the decades, the BCT of today connects 37 towns in an almost continuous network of green spaces. Some gaps remain, but under the management of the Bay Circuit Alliance, AMC, and the Trustees of Reservations, the trail continues to grow and develop.

While hardy outdoor lovers can set an ambitious multiday itinerary, the BCT is unique in that it lends itself to bite-sized adventures. Looking for a day hike? A quick paddle? The trail offers plenty of options, all within a 40-mile radius of downtown Boston. Hikers and bikers, nature lovers and history buffs—there’s something for everyone on the BCT. Here are 19 places to start exploring.

Best Farm Animals: Spencer-Peirce-Little Farm (Newbury)

Visit horses, sheep, goats, pigs, and chickens—all fostered here in partnership with the Massachusetts Society for the Prevention of Cruelty to Animals—then check out the 17th-century manor house. Info: Historic New England

Best Trail Running: Willowdale State Forest (Ipswich)

Whether seeking an easy jog or a long run, trail runners will find a route at Willowdale, where more than 40 miles of trails and carriage roads stretch across 3,000 acres. The BCT enters the forest from the north and passes through field, woods, and swamp. So vast and varied is the terrain that your biggest challenge might be staying found. You may want to tuck a trail map, downloadable from the Massachusetts Department of Conservation and Recreation website, in your shorts. In the fall, Willowdale hosts the annual Stone Cat Trail Races, popular 50-mile and marathon events run on a 12.5-mile loop. In the unlikely event that you tire of Willowdale’s trails, Bradley Palmer State Forest is right across the Ipswich River. Info: Mass DCR

Best Hike for Dogs: Appleton Farms Grass Rides (Hamilton)

More than 5 miles of wide, grassy paths radiate from a clearing in the middle of this forested property. Register for a free Green Dogs permit to walk your pet off-leash. One note: Dogs are not allowed at the adjacent Appleton Farms. Info: The Trustees

Best Mountain Biking: Georgetown-Rowley State Forest (Georgetown and Rowley)

From Ipswich to Andover, the BCT passes through a series of state forests, making this one of Massachusetts’ premier areas for mountain biking. In Georgetown-Rowley, you’ll find a mix of fire roads for the novice and rocky, rooty single-track for the more adventuresome. Thanks to AMC and the New England Mountain Bike Association, among others, a new 76-foot boardwalk leads hikers and bikers over the Mill River and a beaver dam, previously impassable at times. From there, you can pedal deep into the forest on 12-plus miles of trail or stick to the BCT for an easier ride. Info: Mass DCR

Best Camping: Harold Parker State Forest (North Andover and Andover)

When you wake up on the wooded shore of Frye Pond, downtown Boston will feel much farther away than a 20-mile drive on I-93. Not many properties on the BCT are equipped for camping, but Harold Parker’s 89 sites let you sleep among the trees. Situated in the southwest corner of the 3,500-acre forest, the Lorraine Park campground is just south of most of Harold Parker’s 35 miles of trail. It’s perfect for an easy car-camping trip with kids. Info: Mass DCR; Bay Circuit Alliance for other camping options

Best View: Holt Hill at Ward Reservation (Andover)

From the 420-foot Holt Hill, you can see across the Merrimack Valley, to Boston’s skyline and beyond. On a clear day, you might even spot hills along the southern section of the BCT, some 40 miles away. Let the Solstice Stones orient you. This large sculpture at the top of the hill indicates the points of the compass, the summer and winter solstices, and the spring and autumnal equinoxes. The BCT passes right over the hill, while 10 miles of surrounding trails include a boardwalk through a rare quaking bog, where you can view orchids and carnivorous pitcher plants. Grab an interpretive booklet at the parking-lot kiosk for help identifying plant life. Info: The Trustees

Best Public Art: Concord River Greenway (Lowell)

A salvaged-granite tower topped with carved stone birds greets visitors to this multiuse, riverside trail in downtown Lowell. Also look for an 800-foot-long cast-iron fence bearing a passage from Henry David Thoreau’s “A Week on the Concord and Merrimack Rivers.” Info: Lowell Land Trust

Best Road Biking: Bruce Freeman Rail Trail (Lowell, Chelmsford, Westford)

This work-in-progress will eventually cover 25 miles through eight towns; you can currently ride a 6.8-mile stretch from Lowell to Westford. Info: Bruce Freeman Rail Trail

Best Trailside Dining: Kate’s Corner (South Chelmsford)

Situated less than a quarter-mile from the Bruce Freeman Rail Trail, Kate’s is a perfect pre- or post-outing stop. Grab a veggie sandwich or ice cream and stroll or pedal over to the orchard picnic area at Red Wing Farm Conservation Area, about a half-mile away via the Freeman trail. Info: Kate’s Corner

Best History Hike: Nashoba Brook (Acton)

Properties along the BCT served as Revolutionary War battlefields (Concord), Underground Railroad routes (Harold Parker State Forest), Industrial Revolution sites (Lowell’s mills), and transcendentalist outposts (Henry David Thoreau’s cabin at Walden Pond). Amid this colorful history, Nashoba Brook stands out for its detailed interpretive information, illuminating the land’s historic value. Signs on the 2-mile, brookside Trail Through Time—portions of which are on the BCT—explain the significance of an American Indian ceremonial site, stone walls, dams, mill remains, and a stone chamber built into a hillside. (Go ahead: Crawl inside.) One kiosk notes the remains of a 19th-century pencil factory, an important player in a competitive local market. Thoreau worked at his family’s nearby factory for much of his life. Info: Acton Conservation Land

Best Wildlife Viewing: Great Meadows National Wildlife Refuge (Concord)

Great Meadows provides a home or a resting spot for more than 200 bird species. Frequent visitors include waterfowl and great blue heron, and the marsh wren has made this one of its only breeding sites in Massachusetts. Deer, beaver, otter, fisher, and muskrat also reside here, as does one of the Northeast’s largest populations of Blanding’s turtle. Easy access makes the refuge hard to top: You can see almost the entire property from the parking lot and the adjacent telescope-equipped observation tower. From the lot, follow the Dike Trail between the Upper and Lower pools. Pause on the banks of the Concord River before completing the 1.7-mile loop of the Lower Pool. The BCT arrives at Great Meadows via the 4-mile Reformatory Branch Rail Trail, meaning you could walk, run, bike, or drive here. Info: U.S. Fish & Wildlife Service

Best Swimming: Walden Pond (Concord)

Walden Pond is popular for good reason. The sandy beach at this 102-foot-deep glacial kettle hole draws crowds all summer long. Best to arrive when the gates open—or, better yet, ride your bike—as the parking lots fill fast. Call 978-369-3254 for seasonal hours. Info: Mass DCR

Best Day Hike: Nobscot Scout Reservation (Sudbury and Framingham)

With uncrowded trails and overlooks more typical of the mountains, Nobscot is one of the BCT’s best escapes. The trail recedes quickly from busy Route 20 in Sudbury. Less than 1 mile in, Tippling Rock provides views of Boston’s skyline to the east and Mount Wachusett and Mount Monadnock to the west and north. In 1.9 miles, the trail reaches the summit of Nobscott Hill, the BCT’s 602-foot high point. Campsites and cabins can be reserved through the Boy Scouts of America. Info: Sudbury Valley Trustees; Boy Scouts of America

Best Cross-Country Skiing: Ashland Town Forest (Ashland)

The BCT zigs and zags for 2.2 miles through this forest’s mixed hardwoods, rocky outcroppings, and wetlands. It’s a quiet, easy option for skiers of all levels. Advanced skiers can extend their route via side trails and the neighboring Cowassock Woods. Info: Sudbury Valley Trustees

Best Fall Foliage: Noon Hill (Medfield)

Beech and oak line the trail up this 370-foot hill. From the top, you can survey the wooded countryside surrounding the Charles River. Plan a hike near Columbus Day (October 10 this year) when foliage likely will reach its peak. Info: The Trustees

Best Family Outing: Moose Hill Wildlife Sanctuary (Sharon)

A year-round calendar of programming for kids and adults, rotating art exhibits, and 25 miles of trails make this a great destination for families with kids of any age. Mass Audubon’s oldest sanctuary—it turns 100 this year—also hosts seasonal events, including a native plant sale in June, a Halloween night hike in October, and a maple sugaring weekend in March. If you prefer to explore on your own, don’t miss the vernal pools, the 700-foot boardwalk through a swamp, and the sanctuary’s 534-foot high point. The BCT covers nearly 3.5 miles here, heading both east and west from the visitor center. Adjacent Moose Hill Farm offers the Rooms in Time Quest, a popular scavenger hunt for kids. Info: Mass Audubon

Best Picnic Spot: Borderland State Park (Sharon and Easton)

Artist and suffragist Blanche Ames and her botanist husband, Oakes, bought Borderland in the early 1900s and used it as their country estate. The state purchased the 1,800-acre property, which straddles Sharon and Easton, in 1971, making the expansive lawn a prime picnic spot for the public. Just watch out for Frisbees: A hole on the park’s disc-golf course crosses the green. The BCT runs 4.5 miles through the length of Borderland State Park, east to west, passing the visitor center and the mansion en route. Tours of the mansion are held monthly, and it makes a cameo in the upcoming Ghostbusters movie. Info: Mass DCR

Best Wetland Hike: Tubbs Meadow Preserve (Pembroke)

Snapping turtles, great blue heron, and a colorful range of dragonflies frequent this former cranberry bog. Watch from an observation platform then get a closer look via a flat, 1.3-mile loop. Info: Pembroke Conservation Commission

Best Paddling: Kingston Bay (Kingston and Duxbury)

For its mix of natural and human history, the BCT’s southern terminus stands apart. Birds and wildflowers draw visitors to the sweeping Bay Farm Conservation Area, the final section of the trail, but further adventure awaits on the water beyond. Nearly four centuries ago, the Mayflower sailed between the barrier beaches sheltering Kingston, Duxbury, and Cape Cod bays. Today paddlers can head south, into Plymouth, to view a life-size replica of the ship, or north, to explore the marshes at high tide. There’s a put-in on the Jones River and another north of the BCT, at Powder Point Bridge in Duxbury. AMC’s Best Sea Kayaking in New England (AMC Books); Info: Town of Duxbury

LEARN MORE

The Bay Circuit Trail Map & Guide contains nine maps and more than 30 recommended trips, while AMC’s Best Day Hikes Near Boston and Outdoors with Kids Boston feature many BCT sites. You can purchase all three publications in AMC’s online store. Read more about the Bay Circuit Trail in A Long Journey, from AMC Outdoors, and at baycircuit.org.