Built in the 15th century on the banks of the River Eske, this solid gray-stone castle was once the chief stronghold for the O’Donnells, a powerful Donegal clan. In the 17th century, during the Plantation period, it was taken over by Sir Basil Brook, who added an extension with 10 gables, a large bay window, and smaller mullioned windows in Jacobean style. Much of the building has survived the centuries, and both the interior and exterior of the castle were beautifully restored in the 1990s. Guided tours run hourly, included in the admission price.