Lough Oughter Keep, Cavan, Ireland

Lough Oughter Castle is a ruined circular castle on a small island in Lough Oughter, 4 kilometres (2.5 mi) east of the town of Killeshandra in County Cavan, Ireland.

While the exact date construction began is unknown, it is estimated to have started in the first quarter of the 13th century.

The last phase of the Castle's life occurred during Irish Rebellion of 1641-53.

In 1649 Owen Roe O'Neill, the commander of the Ulster Army died at the castle. For the remaining years of the rebellion it's leader Philip O'Reilly retained Lough Oughter Castle as an island fortification, holding it a total of 12 years before it was besieged.

Finally, The British Cromwellian forces had defeated the surrounding indigenous Irish armies, pushed the defenses back to the lake, recovered the lake-shore and proceeded to bombard the castle from positions in the townland of Innishconnell. When the castle finally fell in March 1653, it was the last stronghold in Ireland to fall to Cromwell's forces.

https://en.wikipedia.org/wiki/Clougho...