Arenas de Iguña is a municipality in the autonomous community of Cantabria, in northern Spain. It lies in the Iguña valley, a district of Cantabria through which the Besaya river runs.
The municipality is made up of several small population centres rather than a single built-up town, and it serves as one of the main settlements of the Iguña valley. According to the 2007 census, it had a population of 1,927 inhabitants.