Uxama Argaela on the Castro hill Curiosity · Osma, Tierras del Burgo, Soria On a tabular spur an Arevacian community settled around the fourth century BC that came to be one of the largest cities of Celtiberia; it preserves houses cut into the rock, cisterns and the layout of its streets. Photo: Zarateman (CC0) What to see and do in Osma