Wessex Archaeology was commissioned by Amey to undertake an archaeological watching brief on groundworks associated with the repair of a public sewer within the grounds of Knaresborough Castle as a condition of works set by Historic England. The watching brief was located in Castle Yard, the grounds directly north of the Knaresborough Castle ruins on the western edge of the town of Knaresborough (NGR 434931, 456911). The site was bounded to the west by the River Nidd with residential developments surrounding the site to the north, south and east. The area is now a public garden around the castle museum which has some steep undulating slopes although it generally slopes down to the river to the west. The area has various forms of vegetation and trees. A tree was growing directly over the current pipe. Knaresborough Castle likely dates to the 14th century and was used until significant damage was sustained in the English Civil War. Its remains are a scheduled ancient monument. The grade I listed Church of Saint John the Baptist and the grade II listed Court House Museum are both also nearby. The watching brief monitored a single trial hole (c. 1 x 1 x 1 m). The watching archaeologist monitored all excavations within the specified area. No archaeological deposits were encountered. The natural geology was not reached, and all excavation took place within the original sewer cut, with all deposits relating to that cut. No damage to the archaeological evidence of the scheduled ancient monument was noted.