Castillo de San Francisco, Military castle in Las Palmas de Gran Canaria, Spain

Castillo de San Francisco is a military fort with a triangular floor plan located in Las Palmas de Gran Canaria, on the island of Gran Canaria. It has two pointed bastions at its northeast and southeast corners, a central tiled parade ground, and walls built from dressed stone blocks.

The Cabildo of Gran Canaria requested a fort on the Risco de San Francisco in 1595, after Francis Drake's October raid on Las Palmas. In 1600 Philip III issued a royal decree funding the city's fortifications, and work on the castle began in 1601 under engineer Próspero Casola. Construction was still in progress in 1625; a moat and drawbridge were added around 1621.

The fort takes its name from the Risco de San Francisco, the crag behind Triana where it stands; it was also called Castillo del Rey and Castillo del Paso Angosto, after the narrow pass, 15 to 21 metres wide, that ended the plateau and controlled the road inland. From 1898 it served as a military prison until the end of the century.

The fort sits at the end of Camino Real, near the Military Hospital, and can be seen from the outside. A daytime visit makes it easier to take in the stonework and the triangular shape of the structure as you walk around it.

In 1898 a Royal Order decreed the fort's demolition, but it was to stand until a similar new fortification was built nearby; that replacement never came, so the old fort survived. It later served as a military prison until the end of the 20th century.