Penrhyn Castle is a country house in Llandygai, Bangor, Gwynedd, North Wales, constructed in the style of a Norman castle. The Penrhyn estate was founded by Ednyfed Fychan. In the 15th century his descendent Gwilym ap Griffith built a fortified manor house on the site. In the 18th century, the Penrhyn estate came into the possession of Richard Pennant, 1st Baron Penrhyn, in part from his father, a Liverpool merchant, and in part from his wife, Ann Susannah Pennant née Warburton, the daughter of an army officer. Pennant derived great wealth from his ownership of slave plantations in the West Indies and was a strong opponent of attempts to abolish the slave trade. His wealth was used in part for the development of the slate mining industry on Pennant's Caernarfonshire estates, and also for development of Penrhyn Castle. In the 1780s Pennant commissioned Samuel Wyatt to undertake a reconstruction of the medieval house.

Llandygái is a small village and community on the A5 road between Bangor and Tal-y-bont in Gwynedd, Wales. It affords a view of the nearby Carneddau mountain range. The population of the community taken at the 2011 Census was 2,487. Llandygái community includes nearby Tregarth and Mynydd Llandygái and also the pass of Nant Ffrancon.