This subterranean passage, documented by M. R. Colhoun, maintains modest dimensions of 4 feet in both width and height, creating a tunnel that would have required anyone traversing it to stoop or crawl through its stone-lined interior.

Souterrains, from the French meaning 'underground', are mysterious stone-built passages that dot the Irish landscape, typically dating from the early medieval period between the 6th and 12th centuries. These structures served multiple purposes for the communities that built them; they functioned as storage spaces for food and valuables, refuges during raids, and possibly held ritual significance. The Grange souterrain's location beneath cultivated farmland is typical of these structures, which were often associated with ringforts and early settlements where they provided secure, temperature-controlled environments ideal for storing perishable goods.

The archaeological record of this particular souterrain comes from the comprehensive Archaeological Survey of County Donegal, compiled in 1983 by Brian Lacey and his team of researchers. This survey documented field antiquities spanning from the Mesolithic period through to the 17th century, preserving vital information about sites like the Grange souterrain that might otherwise be forgotten beneath the plough. While the entrance to this underground passage may no longer be visible, its presence beneath the fields serves as a reminder of the sophisticated engineering skills of early medieval Irish communities and their ingenious solutions for storage and protection.