Pen-y-Mwd / Aber Castle Mound

Abergwyngregyn, generally shortened to Aber, is a settlement of great antiquity and pre-Edwardian Conquest importance on the north coast of Gwynedd. Its boundaries stretch from the Menai Strait up to the headwaters of the Afon Goch and Afon Anafon. Protected to the east by the headland of Penmaenmawr, and at its rear by Snowdonia, it controlled the ancient crossing point of the Lafan Sands to Anglesey. A pre-Roman defensive enclosure, Maes y Gaer, which rises above Pen y Bryn on the eastern side of the valley, has far reaching views over Irish Sea with the Isle of Man visible on a clear day.

This was the seat of Llywelyn ap Gruffudd, the last native Prince of Wales, whose daughter Gwenllian of Wales was born here in June 1282. His wife, Eleanor de Montfort, died here as a result of the birth on 19 June 1282. In June 1283 Dafydd ap Gruffudd, Llywelyn's brother, who assumed the title of Prince of Wales after Llywelyn's murder in December 1282, was captured at Bera Mountain above the present village.

Abergwyngregyn was one of ten sites chosen for the Welsh Cultural Heritage Initiative in 2009.