Ireland's ancient and mythical Celtic people left legacies that astound and confound. High on a sheer cliff that plunges 200 feet into the Atlantic, Dun Aonghasa is a ring fort on the island of Inishmore. The labor to build this edifice is incalculable. Northeast in County Sligo, the ancient burial tombs of Carrowmore show that there were brains with the ancient brawn. Archeologists continue to make sensational discoveries that show how the site was created with a sophisticated knowledge of geography and astronomy. Many flock here for perceived mystical powers. In County Clare, the moon-like rocky vistas of the Burren are punctuated with ancient tombs and structures made from huge slabs of stone such as Poulnabrone.