Here is a place . . . . . . where you can walk a Civil War-era fort, visit historic lighthouses, explore tide pools, hike lush trails, camp under the stars, or relax while fishing, picnicking or swimming-all within reach of downtown Boston. Youth programs, visitor services, research, wildlife management, and more are coordinated on the park's 34 islands and peninsulas by the Boston Harbor Islands Partnership.
I walk this regularly (at least twice a week). here are some little trails off the beaten path hat nobody uses but the regulars. It can get pretty crowded but the ocean view is amazing, plus heading towards the city as the sun is going down is beautiful.
Damien M. on Deer Island Trail
Nice view if boston city center and harbor islands, especially at sunrise or sunset. Free parking but small. The bad side is that the path is around a sewage station so the smell and the view is quite bad...