Three Rock Mountain is a mountain in Co Dublin, Ireland. It is 444 metres high and forms part of the group of hills in the Dublin Mountains which comprises Two Rock, Three Rock, Kilmashogue and Tibradden Mountains. The mountain takes its name from the three groups of granite rocks at the summit. It was once believed that these features were man-made: for instance, Gabriel Beranger wrote of them in 1780, "I take them to be altars upon which sacrifices were offered […] the regularity which is observed in piling them convinces me they are the work of man, as they could not grow in that position". In fact, the three outcrops are tors: natural geological features produced by the gradual process of weathering. Today, the summit is dominated by the many radio masts and towers that use the site to broadcast their signals across the Dublin area below. The forestry plantations on the slopes consist mainly of Sitka spruce, Japanese larch, Scots pine, Monterey pine and lodgepole pine.

Two Rock is a mountain in Dún Laoghaire–Rathdown, Ireland. It is 536 metres high and is the 382nd highest mountain in Ireland. It is the highest point of the group of hills in the Dublin Mountains which comprises Two Rock, Three Rock, Kilmashogue and Tibradden Mountains. The mountain takes its name from the two granite tors that lie to the south-east of the summit. From the summit, which is called Fairy Castle, there are views of much of the Dublin area from Tallaght to Howth to the north while Bray Head, Killiney Hill, the Great Sugar Loaf and the Wicklow Mountains are visible to the south. The summit area is mostly shallow bog while ferns and gorse cover the lower slopes. The mountain is also an important habitat for red grouse.