The full name of the Río San Juan’s historic fort is La Fortaleza de la Inmaculada Concepción de María, though everyone refers to it simply as El Castillo. Lying on a hillock beside a narrow stretch of the Río San Juan, the fort was built by the Spanish as a defensive measure against the pirates who continually sacked Granada in the seventeenth century. It was more or less effective for a hundred years, until a British force led by a young Horatio Nelson finally took it in 1780, after which it was abandoned for nearly two centuries. The neatly restored structure boasts an interesting small museum with dusty armaments of the period, information on the area’s history and a few random artefacts found during the restoration of the castle, and a library with more than a thousand books on the history of the castle and the Río San Juan area.