Pistyll Rhaeadr is formed by the Afon Disgynfa falling, in three stages, over a 240-foot (73 m)Silurian cliff-face, below which the river is known as the Afon Rhaeadr. The tallest stage is estimated at about 40 metres. It is counted as one of the Seven Wonders of Wales and is a Site of Special Scientific Interest. The 19th century author George Borrow, in his book Wild Wales, remarked of the waterfall:
"What shall I liken it to? I scarcely know, unless it is to an immense skein of silk agitated and disturbed by tempestuous blasts, or to the long tail of a grey courser at furious speed. I never saw water falling so gracefully, so much like thin, beautiful threads as here."