The rath at Ballynacourty, on the Dingle Peninsula in County Kerry, departs from that norm. Its outline is D-shaped, the straight edge running along the north side, and this small geometric oddity turns out to be the part of the site best worth examining. The fosse, a defensive ditch dug around the outside of the bank, survives all the way around the perimeter, but it is along that flat northern edge that it is most intact, preserved largely because a field wall was built along its outer rim at some point, shielding it from the gradual erosion that has softened the rest.

A rath is an early medieval enclosed farmstead, typically built of earthen banks rather than stone, and home to a single family or small farming community. This one measures roughly 32 metres east to west and 25 metres north to south, with a bank about two metres wide and up to 1.75 metres high still standing in places. The entrance gap, 1.6 metres wide, opens through the bank on the south-east side. The interior holds scattered mounds and depressions, though they do not resolve into any clear pattern. Writing in 1954, a researcher named Ashe recorded the site as bivallate, meaning it originally had two concentric enclosing banks, with the outer one already largely demolished by that point. Today no trace of that outer bank remains, and it does not appear on Ordnance Survey maps, so the only evidence for it is that earlier written account. The site sits on a south-facing slope with open views across the surrounding countryside, the kind of position that would have made practical sense for anyone keeping watch over livestock or land.