CASTLEBAR — Sometime around AD 600, a handful of Irish monks decided that the rigors of fasting and penance on the mainland were not exacting enough. Waiting until the seas were calm enough, they are believed to have rowed to Skellig Michael, a small, pyramid-shaped island seven miles off Ireland’s southwest coast. There, the holy men built a monastery and found the raw seclusion they were after. A millennium and a half later, the site’s ruins are one of Ireland’s best-known heritage and tourist attractions, an antique allure made all the more vivid by the colonies of seabirds that flock to the island’s crags and crevices, and by the puffins and gulls sheltering in the monks’ long-abandoned stone structures. But since 2015, some of those visitors are as likely to be dressed as Chewbacca and waving lightsabers as they are to be conversant in the ways of early Christian eremites or the nesting habits of kittiwakes or gannets.