This one, sitting in level pasture on the edge of a westward slope near Ballinrobe in County Mayo, is a square. That alone sets it apart. The enclosure measures almost exactly forty metres on each side, its stone wall still standing to a height of 1.8 metres in places and roughly 0.9 metres thick, though portions have been rebuilt over the centuries. A modern gate has been inserted into the northeast corner, the kind of quiet alteration that signals a site absorbed into working farmland without quite being forgotten.

Square cashels, as these stone-walled enclosures are sometimes called, are considerably rarer than their circular counterparts, and their origins are not always straightforward to interpret. What makes Caherrobert more intriguing still is the presence of a blocked souterrain in the northwest of the interior. A souterrain is an underground passage or chamber, typically constructed from stone, which was used in early medieval Ireland for storage, refuge, or both. This one has been sealed, so its full extent is unknown, but its existence hints at a settlement that was once considerably more complex than the bare enclosure visible today. The surrounding landscape reinforces a sense of considered placement: higher ground rises to the east, while the land falls away to the west, a position that would have offered both shelter and outlook.