That name tells you something: for generations, what has mattered about this feature is its grove of interior trees rather than any deeper question of what the ring itself might be. The enclosure measures roughly 36 metres across east to west, its earthen bank rising about 1.1 metres on the inside and a little more, around 1.4 metres, on the outer face. A narrow fosse, essentially a shallow external ditch, runs around the outside, and a further drain-like feature follows the inner line of the northern bank, concentric with it.

The site appears on Ordnance Survey six-inch maps from 1842, 1904, and 1937, each time shown as a roughly circular enclosure planted with trees, which suggests the wooded interior has been a consistent feature for well over a century and a half. Whether the planting was deliberate landscaping by the occupants of the demesne, or whether trees simply colonised an older earthwork over time, is not clear. The circular bank-and-fosse form, sometimes called a ringfort, was common across early medieval Ireland, typically enclosing a farmstead, though the heavy overgrowth on the southern and western sides makes it difficult to inspect the full circuit. A ringfort is essentially a defended enclosure, usually dating from roughly the fifth to the twelfth century, defined by one or more earthen or stone banks around a domestic space. Whatever the original purpose at Glencollins, the structure has been persistent enough to survive ploughing, grazing, and the attentions of three centuries of farming, and still holds its trees.