The Piscataqua is a river in a hurry: its current ranks among the swiftest of any natural harbour in North America, and the tugboats waiting at the foot of the brick houses are a reminder that you do not sail here lightly. It is by heading up these swirling waters that coastal cruise ships reach Portsmouth, New Hampshire's only seaport, founded in 1623 and proud to rank among the oldest towns in the United States. Four centuries of maritime trade have shaped a dense, delightful downtown that can be explored entirely on foot.

Strawbery Banke, a neighbourhood that turns back time

The port call's main attraction bears the name the first settlers gave the site, charmed by its wild strawberries. On the site of the original neighbourhood, nicknamed Puddle Dock, the Strawbery Banke Museum brings together more than thirty-seven period buildings from the 17th to the 19th century, still on their original foundations. You move from a colonial kitchen where a stew simmers on the hearth to a 1940s grocery store, guided by interpreters who sew, weave or garden using the methods of their century. Each house tells of a different layer of the port's life: merchants, privateers, immigrants and working-class families.

Prescott Park and the river

Right across from the museum, the gardens of Prescott Park run down to the Piscataqua in a profusion of flowers tended with jealous care. The benches facing the river offer the best vantage point for watching the comings and goings of the tugboats and the lift bridge spanning the water to Maine, just across the way. From there, a walk along the shore leads to the old wharves of Ceres Street, from where cruises depart in season for Portsmouth Harbor Lighthouse and the Isles of Shoals.

Market Square, a beating heart of brick

Heading up Bow Street, whose curved façades follow the riverbank, you emerge onto Market Square, dominated by the white steeple of the North Church. Independent cafés, bookstores and designer shops occupy the ground floors; the upper storeys have kept their multi-paned windows and ornate cornices. The town comes alive without ever becoming hectic, and you quickly understand why so many Bostonians come to spend their Sundays here. Food lovers will note that the local culinary scene, built on seafood, enjoys an enviable reputation in New England.

A submarine in a meadow

A singular curiosity a few minutes from downtown: USS Albacore, an experimental submarine from the 1950s, rests on dry land in a grassy basin and can be explored from end to end, from the control room to the cramped bunks. The vessel was built at the Portsmouth Naval Shipyard, still active across the river, which has been building and repairing submarines since 1800. The visit nicely rounds out the day for families or anyone interested in all things maritime.

The essentials at a glance

• The historic centre is within walking distance of the pier.
• Strawbery Banke takes a good two hours; tickets are sold on site.
• Prescott Park is free to enter, five minutes from the museum.
• USS Albacore: about 2 km from downtown, a short taxi ride.

Heading back down the Piscataqua at the end of the day means retracing in reverse the route of all the merchant ships that made the town's fortune. Portsmouth turns one last time in the wake, compact and russet under the setting sun, with the quiet confidence of places that have found their right size and would not change it for anything in the world.