15. The Sacsayhuamán Walls
The Sacsayhuamán fortress in Peru showcases astonishing stonework by the Inca civilization. Massive stones—some weighing over 100 tons—were cut so precisely they fit together without mortar, and not even a blade of grass can slip between them. The methods used to shape and transport these rocks remain hotly debated, adding to the allure of this ancient stronghold.
