Castle Island, Boston, Massachusetts Castle Island is an easy hike covering 2.2 miles with minimal elevation gain, featuring a family-friendly, paved walk around a causeway to a historic fort. The main attraction is Fort Independence, which was built between 1834 and 1851, andyou will walk around an enclosed bay past a beach, a WWII memorial, and then to one of the country’s most famous forts which were built to defend the city of Boston. Keep your eye out for planes overhead from Logan airport as well as kiteboarders zooming around in the bay. This is an excellent option for all ages—the trail surface is pavement with partial railings, smooth, and typically at least 6 feet wide, with accessible parking available. Castle Island also has a beach and a large playground, making it ideal for a scenic waterfront outing.