Dublin Castle

Dublin Castle, smack bang in the middle of this medieval capital, dates back to the 13th century and has stood witness to most of Ireland's most pivotal historical moments. While not all of Dublin Castle is available to visit for free, key parts like the Chapel Royal, the Garda Museum and the Revenue Museum are available to view without charge although you may need to book ahead to ensure a tour space. The aforementioned Chester Beatty Library is one of the most incredible attractions on offer in free Dublin but the grounds of Dublin castle alone are well worth perusing of an afternoon.