Constructed in 1768 (rebuilt 1820) Poolbeg lighthouse is believed to be the first candlepower operated lighthouse in the world. Sitting at the end of Great South Wall it is a perfect walk taking about a 40 minute walk down the pier and again.
Dublin Bay has had a long-running problem with silting, notably at the mouth of the River Liffey. The south (and north) walls were built to allow Dublin be a deep water port. Prior to this, boats had difficulties entering the river due to the silting and sandbanks.
The construction of the wall was completed in 1795 and at the time it was longest sea wall in the world. The view from Poolbeg lighthouse is spectacular. Standing at the end of this pier feels like you are in the middle of the ocean. From this point you have a full panorama of Dublin Bay extensive views of Dublin Port, Dun Laoghaire and Howth.