The example at Greaghnaglogh in County Roscommon applies the same logic entirely inland, using the junction of two streams to create a naturally defended spur of land. The result is a small but surprisingly coherent fortification, its platform of grass and heather sitting some twenty metres above the streams at its southern edge, with the land falling away steeply on three sides.

Where nature left a gap, whoever built this fort closed it with earth. Along the northern approach, the only side without the protection of a natural drop, there is an earthen bank roughly eight metres wide, rising about 1.6 metres on the interior and nearly three metres on the outside face. Beyond that sits an outer fosse, a defensive ditch, curving out to the north in a gentle arc and measuring just over six and a half metres across at its top. The enclosed platform is broadly rectangular, approximately thirty-one metres north to south and thirty metres east to west. Notably, no entrance is visible anywhere on the surface today, which gives the place a quietly sealed quality, as though whatever happened here was meant to stay contained.