A small, rubble-built seventeenth-century house with a rebuilt eighteenth-century S. front and slate-covered roof, Ystum has opposite doorways with wooden-mullioned windows flanking the N. doorway (one blocked). The fireplace has a brick-built oven at its N.E. corner. In the middle o the twentieth century, it was described as in poor condition and as being used for cattle.
(Source: Inventory of the Ancient Monuments in Caernarvonshire, vol. III (RCAHMW, 1964))

A. N. Coward 30.01.2018