Craig-y-Dinas hillfort can be found due east of Dyffryn Ardudwy, overlooking Llyn Irddyn. It is at the summit of a prominent rocky outcrop (1150 feet) and is polygonal in shape and has dimensions of approximately seventy metres by forty metres (0.5 acres). The single wall encircling the fort, and would have been about six feet thick, but it is now collapsed.
There is no evidence of dwellings within the fort but there are the remains of five roundhouses approximately one hundred metres from the fort to the east. There have been no excavations at the site, and it was probably not a permanent residence, but might have been a place of refuge, or meeting place.