It measures approximately twenty metres at its longest and fifteen at its widest, and its surface is covered with trees. To the casual eye it might read as a natural feature of the lake, an accident of geology or glacial deposit. It is almost certainly neither. The island is classified as a crannog, an artificial or heavily modified island constructed by human hands, typically during the early medieval period in Ireland, though some crannogs were in use from the Bronze Age right through to the seventeenth century. They served as defensible homesteads, their isolation providing protection that a promontory or hilltop might offer on dry land.

The compact dimensions of this example are fairly typical of the form. Crannogs were generally built up from layers of timber, peat, brush, stone, and organic material, sometimes anchored with large wooden piles driven into the lakebed. Over the centuries, the original structure becomes absorbed into the island itself, which is why many survive as low, tree-covered humps that attract little attention unless someone is specifically looking for them. The trees now growing on this one in Larkfield Lough have, in a sense, completed the disguise that time began.