Nidd Gorge makes up a section of the River Nidd in North Yorkshire, England, in which the river enters a deep ravine with sheer tree-covered valley sides. The river as a whole flows from its source near Great Whernside in Nidderdale, to its confluence with the River Ouse near Nun Monkton. Nidd Gorge makes up approximately 3 miles (4.8 km) of the entire length of the river, and stretches from the now defunct Nidd viaduct at Bilton in Harrogate to Grimbald Bridge, just south of Knaresborough.