Ruinaulta

Ruinaulta is a canyon on the Vorderrhein just upstream of the Hinter Rhine at Reichenau, Eastern Switzerland. It is sometimes known as the Rhine Canyon, or Swiss Grand Canyon. Protected by cliffs several hundred metres high, the area is forested and a haven for wildlife. It is easily accessible only by the Ruinaulta line of Rhaetian Railways, and is a popular location for rafting.

http://www.ruinaulta.ch/de/welcome.cfm

These snails are the size of golf balls

http://www.rhb.ch/Ruinaulta.776.0.html?&L=4