The interior diameter runs to roughly three metres, which is modest even by the standards of early medieval ancillary buildings, and the shape itself is a quiet clue to its age and purpose.

A cashel is a stone-walled enclosure, typically of early medieval date, used to define and protect a farmstead or settlement. Caherwalsh appears to have been a busy interior space. This particular D-shaped structure sits in the northeast corner of the enclosure, and it is far from alone. Another structure lies approximately eight metres to the west, two further similar structures occupy the southeast corner, and several possible house sites have been identified elsewhere within the same walls. What that density of features suggests is a settlement that was genuinely lived in over time, with different functions distributed across the enclosed ground, rather than a single-purpose or ceremonial space.