Pen Dinas is the name of a large hill by the village of Penparcau, on the coast of Ceredigion, Wales. It is the site of Pen Dinas Iron Age Celtic hillfort which overlooks the sea from a ridge between the Rivers Rheidol and Ystwyth, and stands above the town of Aberystwyth. Enclosing an area of 3.8 hectares, defined by massive rampart and ditched defences, this is one of the largest and most important hillforts in west Wales. Excavations of the site, between 1933-37, pointed to intermittent occupation during the Iron Age.