Time Out says
The former seat of British rule in Ireland, currently exhibiting an evolution of Irish architecture
Originally built in the thirteenth century on the site of a Viking settlement, Dublin Castle has functioned as a military fortress, prison, treasury, court, water station, and head of the English administration in Ireland. It was reconstructed in the seventeenth, eighteenth, nineteenth, and twentieth centuries, leaving behind an amalgam of architectural styles. Many of the surrounding buildings were added in the eighteenth century for administrative purposes. Today, the castle grounds are used for state functions, Presidential inaugurations, and diplomatic visits as well as the occasional cultural performance. Select areas, including the lavish state apartments, medieval undercroft, ornate royal chapel, craft shop, and heritage centre, are also open to tourists.
Time Out tip: If you or anyone of your mates are a history nerd, pony up the few extra Euros for the much more extensive guided tour.
Chester Beatty Library: For a breathtaking journey through more than 20,000 manuscripts, books, paintings, and objects
The Long Hall: For great Guinness and traditional charm dating back to the nineteenth century
Rustic Stone: For an innovative Irish meal made from local produce