Viamala

Viamala or Via Mala is a narrow gorge along the river Hinterrhein between Zillis-Reischen and Thusis in the Canton of Graubünden, Switzerland, as well as the ancient and notorious pathway which traverses the gorge. Historically the Viamala was the most serious obstacle on the approach to the Splügen and San Bernardino mountain passes.

Source: Wikipedia