It is roughly 32 metres across, its interior raised into a gentle dome about one and a half metres high, and ringed by a shallow ditch, an annular fosse, that measures three to four metres wide and only about 30 centimetres deep. That combination of domed centre and encircling ditch is the kind of profile that can belong to several different traditions, prehistoric, early medieval, post-medieval, or none of them in any functional sense. The structure has never been firmly pinned down.

What complicates matters is a single tantalising detail from the cartographic record. The enclosure was already present, and already considered worth marking, when the Ordnance Survey produced its six-inch map of the area in 1838. The surveyors used hachures, the short radiating lines that indicate a raised or sloped earthwork, to capture its outline. That notation tells us the feature was legible as a physical form nearly two centuries ago, but it tells us nothing about who made it or why. One possibility entertained by those who have looked at it is that it may simply be a designed landscape feature, the kind of ornamental earthwork that estate owners occasionally introduced into their grounds during the eighteenth or early nineteenth century. Tulfarris, sitting close to the margins of what is now the Blessington Reservoir, was estate land, and a decorative mound or viewing platform placed within a planted woodland would not have been unusual in that period and context. But that reading remains speculative, and the structure carries no documentation to settle the question either way.