The single most impressive sight on the island, Brimstone Hill is a colossal 18th-century British fortress perched 800 feet above the sea on a volcanic outcrop. It is a UNESCO World Heritage Site and one of the best-preserved historical fortifications in the Americas, with bastions, citadels, magazines, and barracks all built from the black volcanic stone that gave the hill its name.
The views are extraordinary. On a clear day you can see the neighbouring islands of Saba, Sint Eustatius, Saint Barthélemy, and Saint Martin laid out across the Caribbean. The on-site museum covers the colonial wars, the brutal economy of sugar and slavery that paid for the fortress, and the engineering feat of building it. Allow at least two hours; the road up is steep and winding.