Ruins of Dunseverick Castle, County Antrim, Northern Ireland (© Krzysztof Rogalski/Getty Images)

At Dunseverick Castle, history hangs on—literally. Wall fragments cling to a basalt stack above the Atlantic, proving that even ruins can hold their ground. Two thousand years ago, it marked the end of the Slige Midluachra, one of Ireland's five great roads, linking travellers to the royal seat at Hill of Tara. In the 5th century, Saint Patrick is said to have visited and baptised a local man, Olcán, here. Tradition holds that the Lia Fáil (Stone of Destiny), used for crowning Irish kings, was taken from this shore for Scotland.