Fort Independence, a pentagonal five-bastioned, granite fort built between 1834 and 1851, is the dominating feature of Castle Island. This 22-acre urban park is connected to the mainland by both pedestrian and vehicular causeways. Pleasure Bay, the M Street Beach and Carson Beach form a three mile segment of parkland and beach along the South Boston shoreline of Dorchester Bay. Carson Beach offers some beautiful views and great public amenities: a rehabilitated Mothers' Rest, public restrooms, exhibit space, first aid and lifeguard functions, while the outdoor courtyards allow space for passive recreation. Carson Beach also features a walkway which allows one to walk, bike, or run along the water's edge from Castle Island to the Kennedy Library.
Fort Independence and Castle Island are on the State and National Registers of Historic Places. Fort Independence is open from Memorial Day to Columbus Day, hours vary. Fort tours are conducted by the Castle Island Association in the summer months and there is interpretive signage for self-guided tours. The principal program theme, the History of Castle Island, stresses the role of the fort in harbor defense.