Dublin Castle

Dublin Castle was until 1922 the seat of the United Kingdom government's administration in Ireland, and is now a major Irish government complex. Most of it dates from the 18th century, though a castle has stood on the site since the days of King John, the first Lord of Ireland.
The Castle served as the seat of English, then later British government of Ireland under the Lordship of Ireland (1171-1541), the Kingdom of Ireland (1541-1800), and the United Kingdom of Great Britain and Ireland (1800-1922). After the signing of the Anglo-Irish Treaty in December 1921, the complex was ceremonially handed over to the newly formed Provisional Government led by Michael Collins.
Originally built as a defensive fortification for the Norman city of Dublin, it later evolved into a royal residence, resided in by the Lord Lieutenant of Ireland or Viceroy of Ireland, the representative of the monarch.
Inauguration of the first President of Ireland, Douglas Hyde took place in the castle, and the complex has been host to this ceremony ever since. The castle is also used for hosting official State visits as well as more informal foreign affairs engagements, State banquets, and Government policy launches, as well as acting as the central base for Ireland's hosting of the European Presidency approximately every 10 years.