It shares a boundary to the North with Piloña; to the East with Ponga; to the South with León and to the West with Sobrescobio and Laviana.

The municipalities of Caso and Sobrescobio together constitute the Redes Natural Park, designated by the UNESCO as a Biosphere Reserve.

The Natural Monument of the Cueva Deboyu (the Nalón River passes through a cave in the mountain) is also located in Caso.

The AS-17 (Avilés - Pass of Tarna) road is the easiest form to reach Caso from Oviedo or Gijón.

The municipality is located in a wild and mountainous area in which there are plenty of hiking routes and natural places to visit: There is also some old churches and interesting civil constructions.