The entrance, reportedly on the eastern side of the enclosure, was blocked up a couple of generations ago, and the ground has kept its secret ever since. No trace of it remains visible at the surface.

A souterrain is an underground stone-lined passage or chamber, typically associated with early medieval settlement in Ireland, and usually found in connection with a rath, the circular earthwork enclosure that served as a farmstead during that period. The two features were often designed to work together, with the souterrain providing storage, refuge, or a means of escape in times of threat. At Carrownaculla, local tradition preserves the memory of the entrance clearly enough to record its location and orientation, even though the physical opening no longer exists. The blocking of souterrain entrances was not uncommon as land use changed over centuries, whether from practical concerns about livestock falling in, or simply because the passage had ceased to serve any purpose. That the memory survived long enough to be recorded suggests it remained a feature worth talking about within the community, even after it became invisible.