Spaniards, English and Vikings were among the marauders that bedeviled the Irish over the eons. Ancient kings built castles for defense while the invaders built castles to protect their booty. Today you can find these popular stone behemoths across the country. None is more revered than Cashel, a stone edifice on a hilltop that seems designed by castle central casting. You can spend hours wandering its towers and ramparts and strolling the lamb-lined pathways below. Just south, Cahir looks like the model for something you'd build on the beach and is an early example of the English trying to protect their claims.