The church of the little settlement of Casti, halfway up the mountains, is located on a promontory, overlooking the valley of the Hinterrhein, one of the two initial tributaries of the Rhine River. The church dates back to the 12th century. Later the apse was adorned by a large, colourful frescoe, of which only some parts have survived. The frescoe is attributed to an artist (or studio) named "Waltensburger Meister", who worked in the area in the early 14th century.