The Hinterrhein (, ) is one of the two initial tributaries of the Rhine (less in length but bigger by volume) in the canton of Graubünden in Switzerland, flowing from the village Hinterrhein near the San Bernardino Pass through the Rheinwald valley into a gorge called Roflaschlucht. In this gorge an equally sized tributary, the Avers Rhine, adds waters from the deep Val Ferrera and the very remote alp Avers and its side valley Valle di Lei on Italian territory. After the Rofla Gorge, the valley widens into a section called Schams. The Hinterrhein then reaches Andeer, before passing through another gorge, Viamala just before Thusis. Now another tributary of slightly bigger volume reaches the Hinterrhein as the Landwasser, draining a system of valleys, which is commonly known as Davos joins via the Albula coming from the Albula Pass, which is also the name of a railway line that has become a UNESCO world heritage. Another big tributary of Albula river is Gelgia from the Julier pass area. After flowing to Rothenbrunnen through a valley called Domleschg with an incredible number of castles (showing the importance of transit in the area) again the river is left alone from civilisation in the floodplain Isla Bella near Rhäzüns, before it joins the Anterior Rhine at Reichenau, all of them also in Graubünden.