Mentioned by TravelAwaits
17 Fantastic Free Things To Do In Dublin
"The castle is more of a complex with multiple things to see and do. The castle charges admission for the tour, which includes the subterranean view of the River Poddle and of the decommissioned Chapel Royal. That said, tour or no tour, you can plan to take plenty of photos in the courtyard and then go to the gardens to enjoy the Garda Memorial and the Exhibition Hall."