There is no visible entrance to this ringfort at Glasdrumman, which is either a sign of how thoroughly time has softened the site, or a quietly unsettling architectural fact in itself.

A rath, as this type of monument is classified, is an early medieval enclosure, typically defined by one or more earthen banks and ditches, and used as a farmstead or place of refuge. The Glasdrumman example measures roughly 35 metres across its northwest to southeast axis and sits near the crest of a drumlin, one of those smooth, whale-backed hills of glacial deposit that roll across the Irish midlands and northwest. From this position it would have looked out eastward over Lough Allen, the northernmost of the Shannon lakes, about a kilometre away. The enclosure is defined by a slight earthen bank, between three and four metres wide, which survives to an interior height of only 0.2 to 0.4 metres at the southwest and northeast, though the exterior face rises to around a metre. Elsewhere, the boundary survives as a scarp rather than a built bank. On the western to northern arc, a flat-bottomed fosse, or ditch, accompanies the bank; it is nearly six metres wide at the top and a metre deep, which suggests that whatever the earthwork lacked in height it compensated for in the effort required to cross it.