The ringfort at Spinans Middle was never marked as an antiquity on any edition of the Ordnance Survey historic maps; instead, the 1838 six-inch survey recorded it simply as a polygonal-shaped woodland plantation, absorbed into the demesne lands of Kilranelagh House and presumably admired, if noticed at all, as a pleasingly shaped grove.

A ringfort, or rath, is an early medieval enclosure, typically circular or oval, formed by one or more earthen banks and ditches and used as a farmstead or defended settlement. The example at Spinans Middle fits the type, though its history has been complicated by later intervention. What survives is a raised, roughly sub-oval area measuring approximately 60 metres across in both directions, enclosed by a tree-covered bank of earth and stone, with external stone facing still visible in places. Outside that lies a fosse, the ditch that would originally have reinforced the bank's defensive function, and beyond it an outer bank with faint traces of a possible second fosse. A narrow gap in the bank to the north-east, accompanied by a corresponding break in the slope, is likely the remains of the original entrance. Kilranelagh House sits about 300 metres to the south, and it appears the estate's eighteenth or nineteenth-century landscaping absorbed the old earthwork entirely, recasting it as an ornamental tree-ring. Sometime after 1700, a grotto was built directly across the top of the outer fosse on the southern side, a small decorative structure of the kind that became fashionable in designed landscapes of the period, and one that effectively sealed a portion of the earlier archaeology beneath it.

The enclosure remains visible from above as a tree-lined ring, its circular logic still legible even when the ground-level details are obscured by vegetation and centuries of reuse. The bank retains enough of its original form that the essential shape of the place survives, even if its early medieval identity was overlooked for so long that it never made it onto a map as anything other than a wood.