First established by the British in 1771 to mark the dangerous “Londoner” reef, the current granite towers were completed in 1861 and stand 124 feet tall — visible 22 miles out to sea. Designated a National Historic Landmark in 2001, the island is accessible via seasonal boat service from Rockport Harbor. The two towers are positioned so that when a ship sights both lights in alignment, they point to true north — a navigational marvel still appreciated today.