The Castle of San Antón is a fortress on A Pena Grande, a rocky islet attached to the mainland in the mid-20th century. Its construction began in 1588, during the reign of Philip II, on the site of an old chapel dedicated to San Antón and was extended on several occasions, with the neoclassical construction of the governor's house in 1776 being of particular importance. At first, it was used to complete the defence of the port and in fact, it played an important role during Sir Francis Drake’s attack in 1589. It later became a state prison, holding in its cells some famous prisoners, such as the commander Alessandro Malaspina or the liberal general Porlier, who revolted against the absolutism of Fernando VII and was later executed in 1815.
Since 1968 it has been the site of the Archaeological and Historical Museum, which stores important pieces from the prehistory and history of Galicia and A Coruña. The permanent exhibition is organised into three sections: Religious and funerary art, located in the parade ground; archaeology and prehistory, on the ground floor of the governor’s house; and the history of the city, on the upper floor.