Predating the city of Cienfuegos by nearly a century, this fort, to the west of the mouth of Bahía de Cienfuegos, was designed by José Tontete in 1738 and completed in 1745. At the time it was the third most important fortress in Cuba, after those of Havana and Santiago de Cuba.
Extensive renovation in 2010 gave the castle the makeover it sorely needed. In addition to a cracking view of the bay and a basic museum outlining the history of nuclear energy in Cienfuegos (!!), the castle also has a reasonably atmospheric restaurant down below.
Passenger ferries from the castle ply the waters to Cienfuegos (CUC$1, 40 minutes) twice daily, leaving Cienfuegos at 8am and 1pm and returning at 10am and 3pm. Another ferry leaves frequently to a landing just below the Hotel Pasacaballo in Rancho Luna (CUC$0.50, 15 minutes).