Fort Adams, sitting on a peninsula at the entrance to Narragansett Bay, is the largest coastal fortification in the United States — a massive masonry structure begun in 1799 and substantially rebuilt in the 1820s–40s, capable in theory of mounting 468 guns and housing a garrison of 2,400 men. It never fired a shot in anger. The grounds offer the best views in Newport: across the harbor to the city, over the bay to the Naval War College, and out to the Atlantic.
The fort is now a state park and museum, with guided tours covering the labyrinthine tunnels, the listening galleries (underground passages designed to detect sappers), and the history of American coastal defense. The Newport Jazz Festival and Newport Folk Festival are held on the grounds in summer, and the setting — a working fort with the bay on three sides — is spectacular for outdoor concerts. The 1.5-mile perimeter walk around the fortifications is good in its own right, and the parking area on the harbor side has some of the best sunset views in Rhode Island.