A 50 acre island, Thacher Island is 160 feet above the sea and its twin lighthouses have stood watch on a granite ledge over the coasts of Cape Ann since 1771. In the spring, the island, listed as a National Historic Landmark, is home to a nesting colony of Herring Gull and Great-black-backed Gulls. Visitors are able to go inside the North Tower while the South Tower is still an operational tool for the U.S. Coast Guard.