The Castillo de Los Tres Reyes del Morro (Castle of the Three Kings of the Headland, tel. 07/863-7941, daily 8 a.m.–8 p.m., entrance CUC5, children under 12 free, guide CUC1, cameras CUC2, videos CUC5) is built into the rocky palisades of Punta Barlovento at the entrance to Havana’s narrow harbor channel. Canted in its articulation, the fort—designed by Italian engineer Bautista Antonelli and initiated in 1589—forms an irregular polygon that follows the contours of the rocky headland, with a sharp-angled bastion at the apex, stone walls 10 feet thick, and a series of batteries stepping down to the shore.

Slaves toiled under the lash of whip and sun to cut the stone in situ, extracted from the void that forms the moats. El Morro took 40 years to complete and served its job well, repelling countless pirate attacks and withstanding for 44 days a siege by British cannons in 1762.

Originally Castillo de los Tres Reyes del Morro connected with the outside world by sea, to which it was linked via the Plataforma de la Estrella, the wharf at the southern foot of the cliff. Today you enter via a drawbridge across the deep moat that leads through the Túnel Aspillerado (Tunnel of Loopholes) to vast wooden gates that open to the Camino de Rondas, a small parade ground (Plaza de Armas) containing a two-story building atop water cisterns that supplied the garrison of 1,000 men.

To the right of the plaza, a narrow entrance leads to the Baluarte de Austria (Austrian Bastion), with cannon embrasures for firing down on the moat. A cobbled ramp leads up to other baluartes. Various plaques commemorate heroic figures of the siege—even the Royal Navy is honored.

To the left of the Plaza de Armas, the Sala de Historia del Faro y Castillo profiles the various lighthouses and castles in Cuba. Beyond is the Surtida de los Tinajones, where giant earthenware vases are inset in stone. They once contained rapeseed oil as lantern fuel for the 25-meter-tall Faro del Morro (8 a.m.–7 p.m., CUC2 extra), a lighthouse constructed in 1844. Today an electric lantern still flashes twice every 15 seconds. You can climb to the top for a bird’s-eye view of the castle—the climb is tight and not for claustrophobics.

All maritime traffic in and out of Havana harbor is controlled from the Estación Semafórica, the semaphore station atop the castle, accessed via the Baluarte de Tejeda. The harbormaster will invite you up, but you’ll be expected to tip.

Below Castillo de los Tres Reyes del Morro, facing the city on the landward side and reached by a cobbled ramp, is the Batería de los Doce Apóstoles (Battery of the Twelve Apostles). It boasts massive cannons and a little bar—El Polvorín (The Powderhouse).