Sacsayhuamán, an ancient citadel amidst the Peruvian Andes, is an architectural marvel. It was built more than 900 years ago, and no living person knows how such large rocks were fitted so perfectly into walls. This documentary takes us on a tour of Sacsayhuamán, offering a brief history of the site, and clues that may help to its understand how it was made. It was edited from photos and video taken in July 2012, when Russian geophysicists conducted soil research there, at the request of Peru's Ministry of Culture.

• Documentary