The enclosure known as Site 11 sits on a terrace above a low rock cliff on the north-western slope of Knockadoon Peninsula, open to the north-west and backing onto the cliff edge, a C-shaped stone enclosure roughly 27 metres by 25 metres, overlooking the lake towards Knockfennell. It never appeared on historic Ordnance Survey Ireland maps, and for a long time its status in the archaeological record was genuinely uncertain.

The confusion stems from the extraordinary career of Professor Seán P. Ó Ríordáin, who led excavations across Lough Gur over eighteen seasons, uncovering one of Ireland's most significant Neolithic and Bronze Age settlement complexes. An enclosure is, in its simplest form, a defined area bounded by walls or banks, often associated with domestic or agricultural activity in prehistoric communities. When Ó Ríordáin died prematurely, portions of his excavation archive were published posthumously, and it was in that process that the trouble surrounding Site 11 emerged. Scholars O'Kelly and O'Kelly noted in 1978 that Site 11 had reportedly been excavated by Ó Ríordáin, but when Dr Eoin Grogan and Professor George Eogan analysed the archive in 1987, they found that artefacts excavated at the nearby Site 12 had been numbered as Site 11. Some of Ó Ríordáin's records for the area simply cannot be located. Grogan and Eogan described Site 11 as an irregular enclosure of similar construction to Site 12 on the north side of Knockadoon, while noting that no excavation records were known to exist.

The enclosure sits within a dense cluster of prehistoric remains on Knockadoon Peninsula, with Circle K roughly 210 metres to the south-south-west and Site 12 about 280 metres to the south-west, both excavated by Ó Ríordáin. Another unexcavated enclosure lies just 20 metres to the east. Site 11 itself remains unexcavated, its C-shaped outline visible in aerial orthoimages from 2005 onwards, including Google Earth imagery from 2006, 2018, and 2020. The rocky scrub woodland on the north-west-facing slope makes the approach uneven underfoot, and the site is not signposted in the way that Lough Gur's more prominent monuments are. What a careful visitor might notice, looking north-west across the lake from the terrace, is how deliberately positioned the enclosure feels, and how much still lies unrecorded beneath the ground around it.