Scattered across it are several small islands, and among them sits one known as Priest Island, a name that quietly signals a history of religious significance, clandestine practice, or both. Islands with this designation appear at intervals across the Irish landscape, often marking places where Catholic clergy sheltered or celebrated Mass during the Penal Laws of the seventeenth and eighteenth centuries, when open worship was suppressed and priests were liable to prosecution. An island offered obvious advantages: visible approaches from every direction, a natural moat, and the kind of remove that could mean the difference between a secret kept and one betrayed.

Lough Carra itself has a longer history of human presence. The lake and its surrounds were well known to earlier inhabitants of the region, and the broader landscape holds traces of settlement reaching back through the medieval period and beyond. The writer George Moore, who grew up at Moore Hall on the lake's eastern shore, wrote about Carra with an attention to its particular quality of light, and it was here that his ashes were eventually interred on Castle Island. The precise history of Priest Island within this setting, including any structures, burials, or traditions associated with it, remains to be fully documented.