El Faro de Punta Mulas, Vieques

Built by the Spanish between 1895 and 1896 to guide ships safely into the port of Isabel Segunda, the lighthouse at Punta Mulas crowns a modest promontory at the eastern edge of Vieques's principal town — and it's the first thing you see arriving by ferry. Its lantern room sat 68 feet above sea level; the light reached eight miles out, exactly the distance to mainland Puerto Rico. Restored in 1992 and converted into a small museum of island history, it has since been intermittently closed. The harbor view alone earns the walk up.