Set at the confluence of the Rivers Liffey and Poddle, there has always been a fortification of some sort set at the Black Pool that gives the city and castle their name. (Dubh Linn - Black Pool - Dublin) The circular Castle Gardens, with its Celtic knotwork design set into the lawn, sets above the Black Pool itself,... or at least where it once sat. It, and the Poddle run under the streets of Dublin and under the castle, before emptying into the Liffey.
Newgrange (Irish: Sí an Bhrú or Brú na Bóinne) is a prehistoric monument in County Meath, Ireland, located 8 kilometres (5.0 mi) west of Drogheda on the north side of the River Boyne. It is an exceptionally grand passage tomb built during the Neolithic period, around 3200 BC, making it older than Stonehenge and the Egyptian pyramids.
The site consists of a large circular mound with an inner stone passageway and chambers. Human bones and possible grave goods or votive offerings were found in these chambers. The mound has a retaining wall at the front, made mostly of white quartz cobblestones, and it is ringed by engraved kerbstones. Many of the larger stones of Newgrange are covered in megalithic art. The mound is also ringed by a stone circle. Some of the material that makes up the monument came from as far away as the Mournes and Wicklow Mountains. There is no agreement about what the site was used for, but it is believed that it had religious significance. Its entrance is aligned with the rising sun on the winter solstice, when sunlight shines through a 'roofbox' located above the passage entrance and floods the inner chamber
It is the most famous monument within the Neolithic Brú na Bóinne complex, alongside the similar passage tomb mounds of Knowth and Dowth, and as such is a part of the Brú na Bóinne UNESCO World Heritage Site. There are many smaller archaeological sites such as henges, mounds and standing stones situated in the .75 km between Newgrange and the Boyne. Newgrange consists of approximately 200,000 tonnes of rock and other materials. It is 85 metres (279 ft) wide at its widest point.
After its initial use, Newgrange was sealed for several millennia. It continued to feature in Irish mythology and folklore, in which it is said to be a dwelling of the deities, particularly The Dagda and his son Aengus.