Pen y Bryn is a two-storey manor house, in Abergwyngregyn, Gwynedd, in north-west Wales, adjacent to the A55, five miles east of Bangor, eight miles west of Conwy. It is constructed mainly of broken stone, with roughly dressed quoins and a slate roof. The house is situated within Garth Celyn, a double bank and ditch, overlooking the Menai Strait to Anglesey. A smaller house was immediately adjacent in 1811 when Sir Richard Colt-Hoare recorded it; this was demolished by 1815. The present structure incorporates a four-storey stone tower. The present roof timbers were dated by dendrochronology to 1624, when the house was refurbished. There is evidence of long use with multiple rebuildings before 1624, but there is disagreement on the duration and nature of its mediaeval use.