The walls of Sacsayhuaman sit above Cusco, built from stones cut and fitted with such precision that some blocks reportedly weigh up to three hundred tons, and the Incas left no written records explaining how they moved or shaped them. In July 2012, Peru's Ministry of Culture invites a team of Russian geophysicists to study the site's soil and stonework, and the film follows their expedition with footage they shot on location. The researchers collect samples from the ground and from the stones themselves, material they plan to analyze back home to determine what the blocks are made of and how they were joined without mortar. The film sets Sacsayhuaman alongside other Incan sites, from Machu Picchu to Ollantaytambo, stretching across a range from Ecuador to Chile, but treats this wall as the most puzzling of them, dated to the fifteenth century and still resistant to full explanation. The camera lingers on the joints between stones, where the fit is close enough to leave no gap for a blade.