Tabayón del Mongayu Nature · Caso, Nalón, Asturias Image of Caso, not of the place itself. A waterfall hemmed into the beech wood of the Redes Natural Park, reached by a track from Tarna; it was declared a natural monument on 22 May 2003 along with other wetlands and waterfalls of the Asturian mountains. Photo: Crisjerez (CC BY-SA 4.0) What to see and do in Caso