The wilderness jewel of the North Shore  is Plum Island, a barrier island extending for 11 miles along the entrance of Newburyport Harbor. The bulk of the island is taken up by Parker River National Wildlife Refuge (6 Plum Island Tpke., 978/465-5753, www.fws.gov ), a stopover for migratory birds on the Atlantic Flyway. A two-mile trail wends its way through sand dunes and swamps, providing excellent opportunities for bird sightings. It’s also possible to surf-fish from the beach.
The five-mile Marblehead Rail Trail offers beautiful vantages of the ocean and oceanfront mansions, with a two-mile spur into Salem .
Rent bikes from Marblehead Cycle (25 Bessom St., 781/631-1570, www.marbleheadcycle.com ).