Located in the Ticknock area, Three Rock mountain provides give you a great view of Dublin, Bray and the Sugar Loaf. It is 444 meters (1,457 feet) high. There are plenty of trails around this area. Below shows the location of a carpark near the mountain and some photos to enjoy. There are also a number of telecoms structures on the summit as can be seen from the photos.
Coillte have a lot of information on walks in this area, check them out here: http://www.coillteoutdoors.ie/index.php?id=173&trail=272&no_cache=1