In the United Kingdom, the term listed building refers to a building or other structure officially designated as being of special architectural, historical, or cultural significance; Grade I structures are those considered to be "buildings of exceptional interest". Listing was begun by a provision in the Town and Country Planning Act 1947. Once listed, strict limitations are imposed on the modifications allowed to a building's structure or fittings. In Wales, the authority for listing under the Planning Act 1990 rests with Cadw.

Glynllifon is an old estate which belonged to the Barons Newborough, near the village of Llandwrog on the main A499 road between Pwllheli and Caernarfon in Gwynedd, Wales. The original mansion was until recently a privately owned hotel.