This irregular stone enclosure first appeared on the 1836 Ordnance Survey map simply marked as ‘Fort’, though it had vanished from maps by 1905. The site measures roughly 70 metres north to south and 30 metres east to west, with collapsed stone walls defining most of its perimeter; the eastern edge needs no wall, as nature has provided its own defence in the form of a sheer cliff face.

The enclosure takes its evocative name from its location between mountain ridges, with a holy well and cairn sitting in the gap immediately to the northeast. Two substantial standing stones at the southern end likely mark the original entrance, whilst early 20th century archaeologist Boyle-Somerville reported seeing several circular structures at the southeastern corner in 1929, though these features weren’t visible during more recent surveys. The dating and original purpose of this hilltop site remain uncertain, but its commanding position and substantial stone construction suggest it held considerable importance for the communities who built it.

Today, Caiseal Na Bearnan stands as a testament to the ingenuity of Ireland’s early inhabitants, who transformed this challenging mountain landscape into a fortified settlement. The site forms part of County Donegal’s rich archaeological heritage, documented in the comprehensive Archaeological Survey of County Donegal, which catalogues field antiquities from the Mesolithic period through to the 17th century.