The Aceñas de Olivares are a set of restored watermills on the Duero, just below Zamora's old stone skyline. They are not as imposing as the cathedral or castle, but they show the practical river city: grinding grain, controlling water, and using the Duero long before it became a scenic backdrop.
The walk down to the river is worth doing for the view back up toward the walls and Romanesque churches. Inside, the mills explain the machinery and the role of river milling in the city. It is a small stop, but a useful one if you want Zamora to feel like a lived medieval town rather than a collection of isolated monuments.