Made with the page turned horizontally, this is one of three studies in this book of Caernarvon Castle made from a boat in the Menai Strait. The other two are on folios 21 verso and 22 verso (D01941, D01943). Here the boat has moved round to the west, less close in than in the sketch D01943, and preparing to enter the estuary of the River Seiont, where Turner made three more drawings on the versos of folios 24, 25 and 26 (D01947, D01949, D01951). The Eagle Tower dominates the composition in the centre, with the town encircled by its walls in front of the castle, to the left; the mountain in the right background is Moel Eilio. For the Seiont, see the entry for D01947.