It measures roughly 45 metres north to south and just over 43 metres east to west, enclosed by a bank of earth and stone standing about 1.5 metres high, with a fosse, or defensive ditch, cut to a similar depth running around the outer edge from the south-east to the west. It is not dramatic in the way a castle or a tower house is dramatic. What it is, instead, is old in a very particular way, the kind of old that you can walk around the rim of.

This is a rath, the Irish term for a ringfort, a type of enclosed farmstead that was the standard unit of rural settlement in early medieval Ireland, broadly between the fifth and twelfth centuries. Tens of thousands were built across the country, though many have been ploughed out or built over. They were not military installations in any serious sense; the bank and ditch were more likely intended to keep livestock in and wolves out, and to signal status within the community. The Ballynagaul example has gaps in its bank to the north and west-southwest, and a possible original entrance facing the east-southeast, a common orientation that would have caught the morning light. At the centre of the enclosure, a smaller circular bank survives, enclosing an area of about 7.7 metres in diameter. This inner feature is interpreted as the remains of a hut site, probably the footprint of a circular dwelling where the inhabitants of the farm actually lived and slept.