Castyll Forwyn was built in 1867 for the Rev. John Lloyd, rector of Llanmerewig, on grounds purchased from the Earl of Powis. Designed by John Wilkes Poundley and David Walker of Poundley and Walker, the two-storey building is built of yellow brick with slate roofs. The building faces south-west and is entered through a large embattled two-storey porch, to the left and right of which are single storey projecting bays, each with a large window. The right bay is flat-roofed with panelling decorated with lozenges, while that on the left has a pyramidal roof. There are second-storey windows above a string course above the bays and a first storey window to the left of the left bay. The north-west face of the building has a large bay window, the second story of which projects outward beyond the first storey. Since the twentieth century the building has been used as a youth hostel and as a hotel.

(Sources: NMR Site files, Montgomeryshire, Domestic, SO19SE; J. D. K. Lloyd, `The Lloyds of Montgomery?, Montgomeryshire Collections, 49 (1946), 244-61 (260-61); Idem, `John Wilkes Poundley: A Montgomeryshire Architect?, Montgomeryshire Collections, 65 (1977), 47-56 (52); Scourfield and Haslam, The Buildings of Wales: Powys (London: 2013), 110)
A.N. Coward, RCAHMW, 09.05.2018