Holyhead Mountain is at the northern end of Holy Island, Anglesey, jutting out into the Irish Sea.

There are traces of field systems and the bases of dry-stone walls of twenty huts, and there are a number of standing stones in the vicinity.

The material for the breakwater at the port of Holyhead was quarried from the limestone areas of the northeastern side of the island, with seven million tons of limestone being removed from long-established[4] quarries to form the longest breakwater in Britain, at nearly one and a half miles (2.4 km) long.

Views from the summit are extensive, especially to the west, where the Wicklow Mountains in Ireland can often be seen across the Irish Sea on clear days.

Birds that nest here include Atlantic puffins, stonechats and Eurasian oystercatchers, and grey seals can be seen offshore during the summer.