This bivallate ringwork, a double-banked defensive structure, consists of two substantial earthen ramparts arranged in concentric circles, each originally accompanied by its own defensive ditch or fosse. The inner and outer banks create a formidable series of obstacles that would have challenged any attacker, though centuries of weathering and agricultural use have left gaps in both ramparts, with evidence of old quarrying visible near the southeast entrance.

The roughly circular monument sits on a subtle natural elevation, offering a strategic advantage over the surrounding wetlands. A modern field fence now cuts through the site from east-northeast to west-southwest, but the overall layout remains clearly visible, particularly from above; aerial photographs taken in 1966 reveal the impressive scale and design of these earthworks. The southeast entrance gap appears to be original, providing controlled access to the protected interior space.

Within the southern half of this defensive ring stand the remains of Doon Castle proper, suggesting the circular earthworks served as the castle’s bawn, essentially a fortified courtyard typical of Irish tower houses and castles. This arrangement would have provided multiple layers of defence whilst creating a secure area for livestock, supplies, and daily activities. The combination of natural defensive features provided by the marshy ground and the carefully engineered earthworks demonstrates the sophisticated understanding of defensive architecture employed by medieval builders in Ireland.