Altheim is a town in western Upper Austria.Altheim lies in the District of Braunau am Inn in the traditional region of Innviertel of Upper Austria. It also lies on the Mühlheimer Ache, a tributary of the Inn.SightsIn 1985 archaeologists discovered the ruins of a Roman villa in farmland just outside Altheim. In the town there is a Roman museum dedicated to these findings, the Ochzethaus.