The site in Cregganna Beg sits on a rise in rocky scrubland, and measures around 32 metres in diameter. That is not a small structure, but you would be forgiven for missing it entirely: a later field wall has been laid directly over the original drystone construction, and a separate field wall cuts straight across the interior from east to west, slicing through what would once have been an enclosed and purposeful space.

Cashels of this kind were typically built during the early medieval period in Ireland, functioning as enclosed farmsteads or settlement sites for a family group of some standing. The drystone technique, fitted stone without mortar, was well suited to the rocky landscapes of Connacht, where building material was rarely in short supply. What makes Caheracullin of particular note, despite its poor state of preservation, is the presence of a souterrain in the interior. Souterrains are underground stone-lined passages or chambers, likely used for storage or as places of refuge, and they are frequently associated with cashels across Ireland. Later generations apparently found the enclosure's walls more useful as a ready-made field boundary than as something worth preserving, a fate common to many such monuments across the west of Ireland. The site was noted by Holt in 1912 and appears in subsequent surveys by O'Flanagan and McCaffrey across the mid-twentieth century, suggesting it has attracted at least passing scholarly attention even in its diminished condition.