It measures roughly fifty metres east to west and thirty-five metres north to south, and is composed of small stones, the accumulated work of people who built it up from the lakebed, probably in the early medieval period. That construction method is the giveaway: this is a crannog, an artificial or semi-artificial island dwelling of a kind used across Ireland and Scotland from the Bronze Age well into the medieval period, typically serving as a defensible homestead surrounded by water rather than walls.

What gives the site an additional layer of strangeness is a passage recorded in the Annals of the Four Masters for the year 990 AD, cited by the historian James Hardiman in 1846. The entry describes how "a great wind swallowed the Island of Lough Kime suddenly in one hour, with its habitation and circular wall, which was thirty feet." Whether Lough Kime refers to this same body of water, and whether the event describes a storm, a structural collapse, or something stranger in the telling, is left unresolved. Animal bones recovered from the site suggest sustained occupation at some point, consistent with the everyday domestic activity typical of crannog life. Then the island's history takes an abrupt turn in tone. On the northwest and southeast sides stand two summerhouses dating from the eighteenth or early nineteenth century, almost certainly connected to the nearby Lisdonagh House. The same small island that may once have carried a circular palisade wall was later furnished with genteel garden buildings, the kind of ornamental follies that Georgian landowners placed in landscapes they were reshaping for aesthetic pleasure.

The juxtaposition is quietly odd: early medieval habitation, a medieval chronicle entry about catastrophic destruction, animal bones in the soil, and then two summerhouses arranged like punctuation marks on either side of the island. The crannog endured, or was reused, or was simply convenient, and the trees that now cover it hold all of that layering together without giving much of it away.