Sitting roughly 260 metres from the eastern shoreline in the broad stretch of Rochfort Bay, this oval islet is a crannóg, an artificial or partly artificial island constructed in a lake, typically for settlement or defence. It rises to about 3.5 metres above the waterline and measures approximately 35 metres east to west and 25 metres north to south. The construction is deliberate and layered: large boulders forming the base, smaller stones packed towards the waterline, with some angular blocks that may have been quarried rather than gathered. The east face, closest to dry land, is steeply sloped and notably bare of timber, while the lakeward sides still show horizontal and vertical timbers just at the waterline.

What makes this site particularly striking is the complexity of the defensive works revealed by underwater survey. Around the northwest, west, and southwest sides of the island runs a horseshoe-shaped palisade of 149 posts, a palisade being a fence-like barrier of driven timber stakes, here arranged in rows of two and even three at certain points, extending as far as 20 metres out from the island's edge. Two narrow gaps in this outer barrier align with a stone jetty roughly eight metres in diameter, suggesting a controlled, possibly guarded entry point. The palisade does not extend around the eastern, shoreward side, and the water there is notably shallow. A radiocarbon date from the palisade timbers places construction in the ninth century. Beneath the surface, six small stone platforms, three to the north and three to the south, add further complexity to the submerged landscape around the island. Researchers working on the Crannog Archaeological Project noted the close similarity in plan and construction between this site and a neighbouring crannóg, Cró Inis, elsewhere on the lough, suggesting these were not isolated endeavours but part of a coherent pattern of lake-based occupation in early medieval Westmeath.