Pen Dinas is a large hill in Penparcau, on the coast of Ceredigion, Wales, upon which an extensive Iron Age, Celtic hillfort is situated. The site can easily be reached on foot from Aberystwyth town centre and is accessible via a series of well marked trails. Boasting a commanding position at the confluence of the River Ystwyth and Afon Rheidol, it has been described as "the pre-eminent hillfort on the Cardigan Bay coast".