I recentrly visited Vikos gorge in the north of Greece. Here is a snippet from wikipedia and a short video I recorder up there:
The Vikos Gorge (Greek: Φαράγγι του Βίκου) is a gorge in the Pindus Mountainsof northern Greece. It lies on the southern slopes of Mount Tymfi, with a length of about 20 km, depth ranging from 120 to 490 m and a width ranging from 400 m only a few metres at its narrowest part.
Vikos is listed as the deepest gorge in the world by the Guinness Book of Records among others. This follows a somewhat arbitrary definition of a gorge that excludes deeper features such as Colca Canyon because of their greater width:depth ratio.