Rhiwlas Hall, a twentieth-century house on a more ancient site (nprn 28709), is located within a small but well-preserved landscape park on the east bank of the Afon Tryweryn (700264). The house is surrounded by gardens which date largely from the nineteenth century. These are largely informal and form two contrasting parts: the steep rockery, lawn and shrubbery to the west of the house, and the woodland walk and semi-formal gardens to the east.

The western area contains planting post-dating the 1860s, and the rockery of probable late nineteenth or early twentieth-century date with earlier elements including sixteenth-century walling. The rockery has largely disappeared but was once extensive with plantings of shrubs and trees. Underplanting includes holly, box and yew.

The flatter area to the east of the house is mostly taken up by the kitchen gardens (700265). Most of the rest is given over to nineteenth-century shrubbery or woodland walk. The shrubbery and the area north of the east drive are probably on the site of natural oak woodland. Some old oaks are left in place with other trees planted at different times, including yew, holly, a purple-leaved type of prunus, birch, firs and acers. The older shrubs consist mainly of rhododendron and laurel. Other features in this area, to the south of the walled gardens, include an area of lawns and ornamental plantings taking advantage of a warm sunny spot both for growing roses and other plants which need an open situation, and for recreational purposes. Most notable is a group of giant sequoias, or Wellingtonias, in unusual numbers. These, and big firs in the shrubbery and some of the older other conifers, were planted in the 1860s.
There are some small, more formal areas of garden near the house.

Sources:
Cadw 1998: Register of Parks and Gardens of Special Historic Interest in Wales: Conwy, Gwynedd & the Isle of Anglesey, 292-5 (ref: PGW(Gd)25(CON)).
Ordnance Survey second-edition 25-inch map: sheet Merionethshire XIV.15 (1901).

RCAHMW, 18 June 2022