Lakeside Ross Castle dates to the 15th century, when it was a residence of the O'Donoghue family. The entertaining 45-minute guided tour combines an easily digested history lesson with real insight into life in medieval Ireland. The castle is a lovely 2.6km walk or bike ride southwest of the St Mary's Cathedral pedestrian park entrance; you may well spot deer along the way.
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Ross Castle
Top choice in Killarney National Park