Which Inca fortress near Cusco is known for its massive stone walls?

The Inca fortress near Cusco known for its massive stone walls is Sacsayhuamán.

Sacsayhuamán is a fortified citadel on a hill above Cusco, Peru, the historic capital of the Inca Empire. The Imperial Inca expanded the site during the 15th century, traditionally during the reigns of Pachacuti and his successors. Its most famous feature is a series of enormous zigzag terrace walls built from precisely cut stones fitted together without mortar.

The largest blocks weigh an estimated 128 to nearly 200 tonnes, and many stones interlock so tightly that even a sheet of paper cannot fit between them. The walls also lean slightly inward, a design that helped them withstand the earthquakes common in the Cusco region. The complex included terraces, towers, storage areas, ceremonial spaces, and a large plaza.

Although often called a fortress, Sacsayhuamán likely had both military and ceremonial functions. After the Spanish conquest, much of the complex was dismantled and its stones were reused in colonial Cusco. The remaining ruins are still used for celebrations including Inti Raymi, the Inca Festival of the Sun, held annually on June 24.

Sacsayhuamán and the city of Cusco were jointly designated a UNESCO World Heritage Site in 1983.