The castle is perfectly adapted to an uneven area, located approximately 70 meters above the sea. It is accessed through a fixed wooden bridge that replaced the original heavy drawbridge, spanning a deep dry moat. Thick stone walls are sharply angled to each other. The castle is spread over levels that run out to the sea in terraces, one above the other, and they are linked by a series of stairs and ramps, giving a sense of the labyrinth. It has three large bulwarks to house the artillery, and a large warehouse that was cut directly into the rock.

The lowest level, located just above the tide mark, is the oldest part of the castle, called as El Revellín La Lengua del Agua (Ravelin of the Tongue of the Water). This ravelin that was built on the narrow promontory, protruding into the sea, existed before the construction of the castle, and for years it served to control the maritime traffic of the Bay of Santiago de Cuba. This part underwent a thorough fortification in 1590. It consists of a firing platform for canons, powder magazine, a guard post, and a command building.

The second level is La Plataforma del Santísimo Sacramento (Platform of the Blessed Sacrament) that includes weapon emplacements, a powder magazine, and quarters for its garrison.

Above this level, there are the El Aljibe, De Adentro and Napoles platforms that have two wide bastions rising on the north and south walls. The whole level was rebuilt in the mid-eighteenth century, and the bastions were added at that time. The lowest and the middle levels are connected by rather steep stairs; risky, but worth to climb to have a good sight.

The highest level of this strategic building is La Plataforma de la Santísima Trinidad (Platform of the Holy Trinity) that was built in 1660s. To the north lies Fuerta de la Avanzada (Avanzada Fort, its architect was Agustín Cermeño) that is located 10 meters above the sea level and at an intermediate point between the San Pedro de la Roca Fortress and another fortress, la Fortaleza del Estrella (Fortress of the Stars), built by the architect Juan de Císcara Ramírez in 1664. La Estrella Fortress has several defense platforms, located on different terraces, and it was guarded by about 80 soldiers and artillery. This chain of fortresses forms a circuit, so that the fortresses support each other and augment the defense by crossed shots. In 1840 the Chapel of Santo Cristo and the Lighthouse were built on this level. The chapel maintains the original wooden crucifix of the 16th century. Two batteries, Scopo Alta and Vigia were added at the time of Spanish-American War in 1898. In general, the castle has many embrasures to defend itself by artillery and numerous loopholes to run fire with the rifles.

The Castle of San Pedro de la Roca, with its associated batteries, is of exceptional value, because they constitute the largest and most complete example of the principles of Renaissance military engineering adapted to the demands of the European colonial power in the Caribbean. It combines the characteristics of two architectural styles:  the medievalism, observed in the thickness of the walls, hermeticity of the rooms, few buttresses, vault ceilings; and the Renaissance, observed in the drawbridge and the dry moat, as well as in the symmetry of the blocks. On the other hand, the castle represents the most complete and best-preserved example of the Spanish-American school of military architecture in Cuba in which its geometric shape, symmetry and proportionality between sides and angles predominate. 

Its authenticity is high, as it underwent few changes since the 19th century.

In the castle there is an expansive parade ground with cannons, trained out to the sea. Now home to the Museo de la Piratería, El Castillo del Morro is also notable for its daily cannon-firing ceremony, which takes place at dusk, but the real splendor here is its superb views out to sea and the city of Santiago de Cuba.