Penrhyn Castle, an early nineteenth-century neo-Norman castle (nprn 16687), is located on the Menai Strait, to the north of Llandegai. It lies centrally within a roughly circular landscape park (700208) and is surrounded by well-preserved gardens laid out during the nineteenth century by the Pennant family, in an exceptional setting against the landscape of north Wales, enhanced by the uncluttered layout. They are now maintained by the National Trust with much new planting though their character is unchanged. 

The gardens consist mostly of informal lawns, planted with specimen trees and shrubs; there is an exceptional collection of woody plants. An estate map of 1768 shows formal gardens surrounding the old house, which must have been to some extent cleared when the present house and outbuildings were built.
Wooded areas and shrubberies lie a short distance to the south of the castle and on a knoll to the north-west. The lawn west of the house was planted with specimen conifers, some of which survive, including one planted by Queen Victoria in 1859. On the south-east side of the castle is The Barbican, a partly grassed terrace in front of the main entrance, with a stone parapet above a steep drop to the drive and park. From the terrace are extensive views across park, coast and hills. To the south of the house there is a south-facing slope, edges undefined, informally planted with tree heathers under mostly evergreen trees. There is an extensive network of paths throughout the garden, some new, others following older routes. They include the Rhododendron Walk.

A ruined chapel to the west of the castle is now a garden feature, but was originally (from the fourteenth century) the family chapel. It was later moved from its original position and is now sited as a romantic ruin (43682). A formal walled terraced garden lies about 230m west of the house (16692) and a kitchen garden is located about 400m to its north (700209). Both probably post-date the building of the house and both are well hidden by trees.

Sources:
Cadw 1998: Register of Parks and Gardens of Special Historic Interest in Wales: Conwy, Gwynedd & the Isle of Anglesey, 250-7 (ref: PGW(Gd)40(GWY)).
Ordnance Survey second edition six-inch map: sheet Caernarfonshire VII.SW (1887).

Penrhyn Castle, with its park and gardens, is part of the Slate Landscape of Northwest Wales World Heritage Site, Component Part 1. Penrhyn Slate Quarry and Bethesda, and the Ogwen Valley to Port Penrhyn. Inscribed July 2020.
It is now a World Heritage Site https://www.llechi.cymru/