 The sanctuary lies within Massachusetts Bay, east of Boston, east of Gloucester, and north of Provincetown, Massachusetts.The heart of the sanctuary is Stellwagen Bank, an underwater plateau stretching north to south, and six miles (10 km) across at its widest, near the southern end.The bank is, on average, 100 to 120 feet (30 to 40 meters) below the surface, while surrounding waters to the west are over deep and to the northeast as deep as 600 feet (200 m).