The interior has been deliberately cut into the hillside to the north-east and built up on the south-west, so that the living surface inside sits roughly level despite the gradient of the slope. It is a small but telling piece of engineering, the kind of practical ingenuity that tends to go unnoticed when people think about early medieval construction.

The fort at Moneycusker is a roughly circular enclosure, measuring 36 metres north to south and 34 metres east to west, with an earthen bank that reaches an internal height of 3.5 metres at its maximum. Outside the bank runs a fosse, a defensive ditch, which survives to a depth of 2.4 metres and is best preserved along the north-east and east sides, where the earthworks remain sharp and well-defined. Elsewhere the sides of the fosse have softened and eroded with time. Along the north-east stretch of the bank, a stone wall has been built on top, absorbed at some point into the surrounding field fence system, which means centuries of agricultural use have quietly overlaid the original structure. The entrance, 4 metres wide and positioned to the south-south-east, is causewayed, meaning a raised crossing over the ditch, and is revetted on its eastern side by two large stones still embedded in the bank, giving some sense of how the threshold was once finished and formalised.