A souterrain is an underground stone-lined passage or chamber, built during the early medieval period, typically between the seventh and twelfth centuries. They are found across Ireland in their hundreds, usually associated with ringforts or settled farmsteads, and their precise function is still debated. Storage, refuge, ventilation for a dwelling above, perhaps all three at different times. The one at Grange is noted as a monument, which at minimum tells us that something was identified here, mapped, and considered significant enough to protect.

Grange itself sits in the shadow of Benbulbin, in a part of Sligo where early medieval settlement left a considerable mark on the landscape. The area has long been associated with some of the densest concentrations of archaeological sites in Connacht, and a souterrain in this townland would fit a familiar pattern of subsurface construction that once supported a farming community, a family, or a small defended enclosure. Without further detail on this particular example, it is difficult to say more about its scale, its construction, or whether any finds were recovered in association with it. What is clear is that it exists as a recognised site, quietly undisturbed beneath ground that has been farmed and walked across for centuries without most people knowing what lies beneath it.