This slight sketch appears to show the inside of Peak Cavern, below Peveril Castle at Castleton, which is seen on adjacent pages. The subject on folio 37 verso (D22219) is positively identified as Peak Cavern by an inscription. The orientation of the present drawing is somewhat unclear, but it is probably horizontal and inverted relative to the sketchbooks foliation; it continues a little onto folio 37 recto opposite (D22218). The shallow diagonal lines may indicate rays of light, or perhaps a sense of general darkness within the cave. For other views of the castle, village and cave, see under folio 1 verso (D22152).