²The souterrain at Donaghmore, just outside Dundalk, is also accessible. It is listed as a National Monument, although it is on private property. Visitors must provide their own lights. It has been described as, "...an elaborate dry-stone structure with traps, a secret passage and vents, built into a trench dug into boulder clay and, in places, into the underlying Silurian grit. The passages and terminal chamber total some 80 metres long, and they are both corbelled and lintelled."
According to Nancy Edwards, there are "upwards of 1,000 examples" of souterrains in Ireland. (Edwards, Nancy. The Archaeology of Early Medieval Ireland. Philadelphia: University of Pennsylvania, 1990. 29.)