A cashel is a dry-stone ringfort, a form of enclosed settlement common across early medieval Ireland, though the one on Scanlan's Island has survived poorly enough that pinning it to any particular period is difficult. Within its remains, the outline of a rectangular house, roughly six metres long and three and a half metres wide, is just about legible beneath the vegetation and tumbled field stones that have accumulated on top of it.

What makes the structure quietly curious is less what it is than where it sits. The island is reachable from the mainland to the north-east, but only at low tide, which would have made it a naturally sheltered and defensible place to settle, close enough to the shore to be practical, far enough to offer a degree of separation. The house occupies what would have been a sheltered corner of the cashel enclosure, suggesting whoever used it understood the logic of the site, tucking a dwelling into the angle of the walls for protection from the wind off the water. Beyond that, the record goes quiet. The date is indeterminate, the builder unknown, and the stones offer no further information than their arrangement.