Ross Castle

Ross Castle perches in an inlet of Lough Leane. It is likely that the Irish chieftain O’Donoghue Mór built it in the fifteenth century.Legend has it that O’Donoghue still slumbers under the waters of the lake. Every seven years, on the first morning of May, he rises on his magnificent white horse. If you manage to catch a glimpse of him you will enjoy good fortune for the rest of your life.Ross Castle was the last place in Munster to hold out against Cromwell. Its defenders, then led by Lord Muskerry, took confidence from a prophecy holding that the castle could only be taken by a ship. Knowing of the prophecy, the Cromwellian commander, General Ludlow, launched a large boat on the lake. When the defenders saw it, this hastened the surrender – and the prophecy was fulfilled.
heritageireland.ie/places-to-visit/ross-castle

Built in the 15th century on the banks of Lough Leane, Ross Castle is open to the public during the summer, but it's exterior can be enjoyed at any time of the year. A must place to visit if you are in Killarney. Not just to see the medieval fortress, but also its lake and mountainside setting.