Mentioned by Dublin 2 days itinerary
The Perfect Dublin Itinerary
"These include the Irish government state apartments, which are used for official state engagements, as well as the Garda (Irish police) Museum and the Chester Beatty Library museum. All of these can be visited. Visiting the main Castle, which includes the State Apartments, requires a ticket, and you can either do a self-guided tour or a guided tour. The former is free for holders of the Dublin Pass."