The island itself is modest, barely eleven and a half metres across and less than a metre above the waterline, overgrown and easy to overlook from a distance. What makes it worth attention is precisely that hidden connection to the land, a piece of deliberate engineering designed to be traversable on foot while remaining concealed from anyone who did not already know where to step.

The island is a crannog, a type of artificial or partially artificial island dwelling used in Ireland from the Bronze Age through to the early modern period. They were typically built by piling timber, stone, peat, and brushwood into shallow lake margins, then often surrounded by a timber palisade. The Glebe example sits at the mouth of a subrectangular bay at the north-eastern end of Fenagh Lough, a subcircular lake running roughly eight hundred metres across its longest axis in south County Leitrim. The causeway, just a metre wide, curves rather than runs straight, a detail noted by Kane as far back as 1886 and one that may have been deliberate, making the safe crossing harder to follow quickly by anyone unfamiliar with its line. The curving approach would slow a pursuer, or mislead them entirely into deeper water.

Fenagh Lough is not a large or dramatic stretch of water, which makes the crannog feel all the more self-contained, a small defended world within an already quiet landscape. The island is stony and overgrown today, its original structure largely obscured, but the proportions recorded suggest it was always compact, a place for a household or a small community rather than a settlement of any scale.