Holyhead Mountain (Welsh: Mynydd Tŵr, meaning tower mountain) is the highest hill on Holy Island, Anglesey, and the highest in the county of Anglesey, north Wales. It lies about three kilometres west of the town of Holyhead, and slopes steeply down to the Irish Sea on two sides. There is a late Roman watchtower, called Caer y Tŵr (Tower Fortress) on the east side of the hill. Holyhead Mountain also has an Iron Age Stone Circle settlement and the material for the Breakwater was quarried from the Mountain too.
Holyhead Mountain attracts many visitors, and it is also located close to South Stack lighthouse; many people come to see the variety of birds which nest along the cliff faces near South Stack.