Castle del Príncipe, Military fortress in Loma de Aróstegui, Cuba

Castle del Príncipe is a pentagon-shaped fortress perched on Loma de Aróstegui with two bastions and supporting defensive structures forming a geometric pattern. Deep trenches encircle the entire structure, and numerous cannons of varying sizes once guarded its positions.

Construction began in 1767 following the English siege of Havana, with Colonel Silvestre Abarca y Aznar from Navarre directing the work. The fortress was built to prevent further invasions and became a critical defensive asset for the colonial port.

The castle is named after Charles of Bourbon, Prince of Asturias, son and future successor of King Charles III of Spain. As a prison it held José Martí's teacher Rafael María de Mendive, Julio Antonio Mella, Eduardo Chibás, Raúl Roa and Juan Marinello, and in 1961–1962 survivors of the Bay of Pigs Invasion were held here until ransomed on Christmas Day 1962. Since the 1970s it has served as a military ceremonies unit.

The fort stands on the Loma de Aróstegui, and its position once gave a view across the city as far as the remains of the old city wall from the Campo de Marte. It faces Avenida Salvador Allende, formerly Avenida Carlos III, the road that led to the Quinta de los Molinos, the Captains General's rest house. The garrison area was built to house 1,000 soldiers.

The castle's red brick tunnels linked the main structure with every outpost and remote position. The fort also held a cistern and quarters for a garrison of 1,000 soldiers, and its defensive artillery counted 60 cannons of various calibers.