The view from the tower is spectacular. You see Howth harbour, Ireland's Eye and miles of sea. Martello Tower is one of many towers that were built along the coast of Dublin during the 19th Century.
Howth Head (Ceann Binn Éadair in Irish) is a headland north east of Dublin City. Entry to the headland is at Sutton, a residential suburb of Dublin, while village of Howth and the harbour are on the northern shore. Originally an island, Howth Head is connected to the mainland via a narrow strip of land, and forms the northerly bound of the great crescent of Dublin Bay, roughly corresponding to Killiney Hill in the south. As one of the northern termini of the DART, Howth is a popular destination for day-trippers from the capital. Hikers can choose from a wide range of routes, including the Cliff Walk or making for the ancient cairn on one of Howth's several summits. On clear days, the Wicklow Mountains can be seen, with Dublin city below. Slieve Donard, an 852 metre peak in Northern Ireland may also be visible. Quite frequently, Snowdon in Snowdonia National Park in Wales can also be seen. Howth Head is also the location where Leopold Bloom proposes to Molly in James Joyce's Ulysses. Howth village (from Old Norse: Hovuð meaning "head", called in Irish: Binn Éadair) originally just a small fishing village and surrounding rural district, is now a busy suburb of Dublin, with a mix of dense residential development and wild hillside, all on the peninsula of Howth Head which is connected to the rest of Dublin via a narrow strip of land. Howth is also home to one of the oldest occupied buildings in Ireland, Howth Castle. The island of Ireland's Eye, Special Area of Conservation, lies about a kilometre north of Howth harbour, with Lambay Island some 5 km further to the north. A Martello tower exists on each of these islands with another tower overlooking Howth harbour and another tower at Red Rock, Sutton. These are part of a series of towers built around the coast of Ireland during the 19th century. from wikipedia