It looks natural enough, roughly 45 metres by 25 metres, rising about two metres above the water, its surface tangled with pine, whitethorn, and ash. Bedrock breaks through in places, and a natural spur juts out into the lake from the south-east corner. But running from the island to the shore is a carefully constructed causeway, eighteen metres long, built from a double row of boulders and measuring only fifty centimetres across, which is puzzling in itself, since the island is already connected to the land by that natural spur. Somebody went to the trouble of building a formal approach to a place that did not strictly need one.

The site sits within a cluster of early medieval features that together suggest this stretch of shoreline was once a place of considerable importance. Some 160 metres to the south-west lies a genuine crannog, the artificially constructed island known as Coolure Demesne 1, the kind of defended lakeshore settlement built and occupied across Ireland during the early medieval period, roughly the fifth to twelfth centuries. A ringfort, another form of enclosed settlement typical of the same era, stands 100 metres to the north-west. The island itself, classified by the archaeologist Aidan O'Sullivan as Coolure Demesne 3, appears to have been a natural feature that was deliberately modified and formalised. The kerb of boulders along its northern edge defines it clearly from the shoreline, and the L-shaped causeway, turning eastward five metres out from the island, seems designed to give it a particular kind of presence. O'Sullivan has suggested that the enhanced island's position directly opposite the constructed crannog may have amplified the social and ideological weight of that neighbouring site, lending the whole arrangement a significance beyond mere practicality. A modern concrete quay and steps on the south-west side, along with a field-wall cutting across the island's width, are later intrusions that do nothing to resolve what the place originally meant.