Promenade in parts

Today’s hike proceeds northeast from Long Wharf, through the North End, and across the Charles River Dam to Charlestown, tracing the outlines of wharves. Luxury hotels and condos dominate, with exceptions like the Boston Fire Department’s Marine Unit on Burroughs Wharf and the US Coast Guard Base in the North End. Battery Wharf, a defensive outpost since the 1600s, is now home to the new Fairmont Hotel, but informative panels keep the site’s history alive.

Intimate gardens provide welcome oases at the ends of warehouses gone condo. But turn a corner, and you may see rotting pilings. Such juxtapositions are the soul of the Harborwalk. Though it has countless scenic passages, it isn’t always pretty, but it is authentic.

Along Commercial Street, clear water laps against refrigerator-sized granite blocks. This may be the most noticeable experience for those who recall the foul water and trashy shoreline before the citizens’ group Save the Harbor, Save the Bay launched the harbor cleanup in the 1980s. Now the water smells fresh, the fish are back, and shopping carts no longer litter the shore. The Harborwalk owes its existence to a cleaner harbor and a Colonial-era law that requires the waterfront to be accessible to the public.

For security reasons, the walk skips over the Coast Guard site, following Commercial Street along the edge of the North End before snaking beneath the North Washington Street Bridge to Charlestown. As vehicles clank overhead, the world feels far away. The intrigue of exploring such hidden realms, however, often occurs in isolated spots that would feel unsafe on a solo outing. Approaching the Charles River locks, the walk crosses alley-cat terrain, a crumbling dock beside us, the Leonard P. Zakim Bunker Hill Bridge suspended beyond. A woman steers a stroller over the dam, where benches face the placid Charles River Basin.

We press on through Charlestown’s new Paul Revere Park, pass Tudor Wharf, and file behind naval cadets marching to the Navy Yard past the USS Constitution, part of Boston National Historical Park. We forgo the remaining mile or so through the Navy Yard and catch a boat from Constitution Plaza to Long Wharf, watch-ing the Charlestown shoreline vanish in a shimmering haze.

Northern Avenue Bridge, part of the industrial waterfront, gets pedestrians to the east side of Fort Point Channel, where the route splits north-south. The north section leads toward the Gillette World Shaving Headquarters. One of the gems here is the space outside the new Children’s Museum. Kids play, moms chat, office workers eat at picnic tables, gazing across at the gleaming Intercontinental Hotel. The museum’s monumental milk bottle ripples in a glass facade on Congress Street. At the channel’s dammed end, a concrete bridge crosses to a new park near Dorchester Avenue, below the huge Post Office. A great half-circle of red metal stands in the park, part of the Old Colony Bridge, “a skewed, sextuple-track triple-warren Scherzer rolling-lift bascule bridge,’’ as a plaque explains.

The south segment of the walk passes the John Joseph Moakley United States Courthouse at Fan Pier en route to the Institute of Contemporary Art. Outside the courthouse, workers hole up with sandwiches in a warren of gardens, hedges, and paths. The walk continues along the wharves of a yet-to-be-developed parcel. At the ICA, we join others on the outdoor bleachers.

Today’s goal is to reach Constitution Beach, near Orient Heights, hitting some new parks en route. The first park, the Airport Edge Buffer, is more attractive than it sounds, pavement glittering with beach glass and stone seats backed with woven rebar. At Jeffries Point, a Harborwalk sign flags Marginal Street as the route, detouring past the active Boston Harbor Shipyard. In the 1830s shipbuilding took off as a big industry in East Boston. One of the most famous yards was Donald McKay’s, on Border Street, which built elegant clippers. (Part of the Harborwalk passes McKay’s old yard.)

Past the shipyard, Piers Park melds architecture and landscape on the former Noddle Island (now attached to land), with pavilions and bench shelters echoing the shallow curves of hulls and gunwales. The Piers Park Sailing Center, which offers free lessons to city kids of all abilities and disabled adults, occupies a dock near the park.

Leaving the rest of this shoreline for another day, we make our way to Maverick Square and the Blue Line. After some urban bushwhacking, we learn that Orient Heights is the T stop for Constitution Beach. This wide arc of sand faces Logan Airport, and the sight of planes landing and taking off mesmerizes a handful of beach sitters.

An electric-blue bridge, its railings shaped into an ecstatic wave, leads back to Orient Heights station, where the whine of the arriving train merges with the whoosh of a plane soaring over the beach we’ve left behind.

On a map, the 2-mile causeway looping around Pleasure Bay resembles a necklace, following the shapely curve of Marine Park and dangling into the blue ocean. The pendant of Head Island hangs at the collarbone point. The shoreward strand leads to the fortified bluff known as Castle Island. It’s a spectacular place to be outdoors.

The path forks to loop around Castle Island, now Fort Independence Park. The five-sided fort, finished in 1851, is the last of several built on this site since 1634. The ocean side of the path leads to a sheltered sunny spot where people sit on benches and in wheelchairs facing the fishing pier, which bristles with poles.

After the Castle Island circuit, we hike Day Boulevard past the L and M Street beaches, where the renovated Depression-era bathhouses open onto separate beaches for men and women, plus a co-ed beach. At Carson Beach, we check out the handsome new picnic pavilion and bathhouse, then turn back and cut up L in search of lunch. Later we pick up the Harborwalk at L Street, which turns into Summer Street and crosses Reserved Channel between cargo piers.

Southbound from UMass, the walk turns left on Morrissey Boulevard, where it crosses a channel, and passes a monument to the Dorchester Vietnam Veterans. After an unfinished stretch of dusty path, we spot a Harborwalk sign across the road. At a crosswalk, we head to Malibu Beach. At the end of the beach, kids on bikes buzz each other at the McConnell Park playground.

We take a side street to Savin Hill Avenue and the Red Line, catching the T to Ashmont, then the trolley to Butler Street and a marsh near the mouth of the Neponset River. Encroaching phragmite reeds, dense and rustling, make this another place where I would not walk alone. A concrete overpass, wire fencing, and train tracks precede a view of the lush estuary, where the river meets salt water. The walk pushes on through the Neponset River Reservation on the far side of Granite Avenue, behind apartment buildings and into Pope John Paul II Park, an expanse of rolling turf noted for kite-flying. No kites in the sky today, but even better, an egret fishes a marshy hollow, oblivious to the people out walking dogs, pushing strollers, riding bikes. After the park, the walk passes under the Red Line trestle, making a right-angle turn at the edge of a restored granite wharf with an ancient pedigree carved into plaques. Passing through the playground at Tenean Beach, the walk returns to Morrissey.

This hike has covered the most diverse terrain in our journey, a metaphor for the varied experiences and connections the Harborwalk has brought to the city, one neighborhood at a time.

Jane Roy Brown can be reached at www.regan-brown.com.