Ross Castle is a knight's tower located on Ross Island on Lough Leane in Killarney National Park. It was the ancestral home of the O'Donoghue clan. Currently, the facility belongs to the state and is open to the public from season to season. The castle has a structure typical of medieval Irish strongholds. The tower was originally surrounded by a square defensive wall, defended by circular corner towers at each end.
The castle was built at the end of the 15th century by the local ruling clan - O'Donoghues Mor. When Olivier Cromwell led his bloody campaign in Ireland in the 17th century, it was the last stronghold to resist him.
There is a legend that O'Donoghue jumped or was pushed out of the window of the great chamber at the top of the castle and disappeared into the waters of the lake along with his horse, table and library. O'Donoghue is said to live now in a great palace at the bottom of the lake, from where he keeps track of what is happening around him.