With an internal diameter of roughly four metres, it is small even by the standards of early medieval Ireland, and the fact that it presses directly against the southern wall of the cashel suggests it was built to make deliberate use of that wall as one of its sides.

A cashel is a stone-walled ringfort, a form of enclosed farmstead common across Ireland from roughly the early medieval period onward, and Caherwalsh appears to have been a busy interior space. This particular D-shaped structure is not the only one. A second lies about six metres to the east, tucked into a corner of the enclosure, and two further structures of similar form occupy the north-east corner. Beyond these, a cluster of possible house sites has also been identified within the cashel interior, suggesting the space was used in a cumulative, layered way over time, with buildings added and rearranged rather than following any single coherent plan. The overall picture is of a settlement that accumulated rather than was designed whole.