The 19th-century Fort Independence sits on 22 acres of parkland called Castle Island (a misnomer, as it’s connected to the mainland). A paved pathway follows the perimeter of the peninsula – good for strolling or cycling – and there is a small swimming beach. Kids get a kick out of watching the low-flying planes heading in and out of Logan Airport.
From the Seaport District, walk south on Summer St for about a half-mile, then turn left on East 1st St and continue to the waterfront.