The crannog at Cullenhugh sits on the north-eastern shore of Lough Iron in County Westmeath, but for most of its existence it would have been surrounded by shallow lake water, roughly twenty metres from the shoreline. A crannog, for those unfamiliar with the term, is an artificial or semi-artificial island, typically built up from timber, stone, and organic material, used as a defended dwelling place from the early medieval period onwards. This one is unusual because it survives as a pair: two conjoined platforms, connected by a short limestone causeway, sitting side by side in ground that is still poorly drained despite the drainage works that transformed the landscape around them. That drainage, carried out on the River Inny in the 1960s, is precisely what exposed them.

Before the Inny drainage scheme, the larger of the two platforms would have been an island; the smaller, ancillary one was partially submerged and appears on earlier Ordnance Survey maps only in part. The drainage lowered water levels enough to strand both structures on dry, or at least dryish, land. Shortly afterwards, the local landowner discovered a dug-out canoe nearby, a find entirely in keeping with the kind of water-based activity a crannog implies. It was during an inspection of that canoe, in the late 1960s, that a man named Joe Rafter first identified the crannog platforms for what they were. A field inspection carried out by Buckley in May 1981 recorded the main crannog as roughly oval, measuring approximately 25 metres north to south and 32 metres east to west, edged with a kerb of large limestone boulders, six of which remain particularly visible on the southern side, each averaging around a metre wide and sixty centimetres high. Inside the perimeter, also on the southern side, are the remains of what appear to be stone house foundations, set in a rough square of about three metres across, with what looks like an entrance from the north. A short causeway of limestone blocks, rising thirty to forty centimetres above the surrounding marsh, connects this main platform to the smaller, circular ancillary crannog, which is about sixteen metres in diameter with its own ring of smaller limestone boulders. Probing of both mounds has revealed hard-packed limestone rubble beneath a layer of habitation soil, dark humus, and charcoal, the typical signature of long occupation. A possible small square structure on the south side of the main platform has been tentatively identified as a duckhide, a low stone enclosure used for concealed wildfowling, though this identification remains uncertain.