There is something magical about sleeping in a castle, surrounded by centuries-old history and royal regalia. In Ireland, the spectacular countryside is graced with brilliantly restored castle properties that fuse sumptuous interiors with 21st-century sophistication. Here, we outline the differences between our four favorite Irish castle hotels—and one very special country estate. These lavish retreats boast five-star amenities, from pampering spas and world-class golf courses to Michelin-starre...