A fortress built in 1617 to defend Acapulco from pirate attacks and is the most important historical monument in the port. The building consists of five bastions that form a five-pointed star when viewed from above, an unusual shape for forts.

It comprises 12 exhibition halls through which the museum aims to connect the inhabitants of the state of Guerrero with the most important moments in its history.

Throughout its galleries, the pre-Hispanic and colonial era history is illustrated. It showcases the colonial defense policy, the pre-Hispanic vestiges of Acapulco, the importance of the port in colonial expansion, the Acapulco-Manila route, the commercial exchange during the viceregal period, an exhibit alluding to piracy, and the Independence hall.

The Historical Museum of Acapulco at Fort of San Diego features advanced museography in twelve permanent exhibition halls, one for temporary exhibitions, an auditorium, a cafeteria, and a bookstore.

The kitchen and chapel of the fort can also be visited.