Guarding a picturesque bend of the River Eske, well-preserved 15th-century Donegal Castle is an imperious monument to Irish and English might. The castle was rebuilt in 1623 by Sir Basil Brooke, along with the adjacent three-storey Jacobean house. Further restoration in the 1990s kicked things into shape; don't miss the magnificent upstairs Great Hall with its vast and ornate fireplace, French tapestries and Persian rugs. Afterwards corkscrew down the spiral staircase to the storeroom. There are guided tours hourly.
Built by the O'Donnells in 1474, it served as the seat of their formidable power until 1607, when the English decided to rid themselves of pesky Irish chieftains once and for all. Rory O'Donnell was no pushover, though, torching his own castle before fleeing to France in the infamous Flight of the Earls. Their defeat paved the way for the Plantation of Ulster by thousands of newly arrived Scots and English Protestants, sowing the seeds of the divisions that still afflict Ireland to this day.