The Museu do Campo Alentejano looks outward from Avis to the surrounding countryside: cork, olives, grazing land, tools, and the rhythms of rural work. It is not large, but it helps explain the landscape you see from the castle and around the Maranhão reservoir.
Pair it with the Order of Avis interpretive centre next door, then leave time to walk through the old streets rather than rushing back to the car.