The house at Derwydd, Llandybie (nprn 17296), is located on a south to south-west facing slope of one of the small valleys made by the Afon Marlais. The walled garden is located to the immediate north of the mansion within the gardens that lie around the house (86150).

The garden is accessed from the house via flights of steps across a narrow terrace, the remains of a former terraced garden now mostly occupied by the walled garden which was possibly extant by 1809. The garden is roughly square, enclosed by rubble walls up to 3m high, and with arched entrances on the east and west in addition to the entrance on the house side. Close to the east and west entrances there are arched, wrought iron growing frames. At the northern end is a small, square summerhouse, built between 1840 and 1887, its front (south) wall forming an integral part of the north garden wall. An adjacent range of building against the outside north wall have gone. 

In the north-west corner of the garden is the site of glasshouses, built before 1905 and now refurbished but with the iron heating pipes (some with humidity trays) and the boiler retained along with the under-floor reservoirs and a mature peach tree.
The interior was laid out with two intersecting paths, a sundial at the centre erected in 1900. Today no fruit or vegetables are grown in the garden but some ancient, cordoned, fruit trees remain against the walls. The interior is now under grass, having been ploughed (aerial images), obscuring the path layout.

Sources:
Cadw 2002: Register of Parks and Gardens of Special Historic Interest in Wales, Carmarthenshire, Ceredigion and Pembrokeshire, 8-12 (ref: PGW(Dy)6(CAM)).
Ordnance Survey County Series 25-inch plan: sheet Carmarthenshire XLI.11 (editions of 1886 & 1906).

RCAHMW, 8 June 2022