The tower keep of Fernán González Monument · Covarrubias, Arlanza, Burgos Image of Covarrubias, not of the place itself. A tenth-century defensive tower of rectangular plan and the shape of a truncated pyramid, with walls of up to four metres at the base. It is the only Castilian fortress earlier than the eleventh century still standing. Photo: Ecelan (CC BY-SA 4.0) What to see and do in Covarrubias