It is slightly lopsided, measuring about 40 metres north to south and 32 metres east to west, and what makes it worth a second look is the survival of two concentric banks with a fosse between them. A fosse is simply a ditch, typically dug to provide the material for the raised banks on either side, and the presence of a double-banked example suggests this was once a more elaborately defended enclosure than the single-banked raths that are the most common ringfort type across Ireland.

Ringforts were built predominantly during the early medieval period, roughly from the fifth to the twelfth centuries, and served as enclosed farmsteads for families of varying social standing. The more banks and ditches a rath possessed, the higher the presumed status of its occupants. The Castlegrove example is in fair condition overall, though the eastern side has not fared as well as the rest; the enclosing elements have been lost there entirely, and several other gaps around the circuit appear to be of modern origin rather than ancient. A field bank radiates outward from the monument at the east, a feature that may reflect later agricultural use of the surrounding land, with the old ringfort boundary pressed into service as a convenient division between fields.