That central depression in the interior of the enclosure may be the only visible sign of a souterrain beneath, a structure that has otherwise slipped entirely from sight.

A souterrain is an underground passage or chamber, typically built during the early medieval period in Ireland, usually of dry-stone construction and covered with large lintels. They are found associated with ringforts, the circular enclosed settlements that were the most common form of farmstead in early medieval Ireland, and their purpose was likely a combination of secure storage and refuge. The ringfort at Maulyregan is a known site in its own right, and the possibility of a souterrain within it adds another layer to what is already a fairly unremarkable-looking piece of landscape. Nothing has been excavated or confirmed; the subsidence in the ground is simply suggestive, the kind of detail that gets noted and then left to sit.