What remains tells a story of a once-substantial defensive structure; short sections of the outer wall face are still visible on the southern and eastern sides, though centuries of decay have made it impossible to determine the original wall thickness. About 10 metres south of the main structure, a natural scarp has been reinforced with large stones, suggesting the site's builders made clever use of the landscape's existing features to enhance their fortification.

The most intriguing feature of this site is a partially accessible souterrain on the western side of the cashel. This underground passage, typical of early medieval Irish settlements, extends for nine metres in a north-south direction before opening at its southern end, where evidence suggests it once continued towards the southeast. The construction showcases the practical engineering skills of its builders; the walls combine large stone slabs with sections of drystone walling, whilst the roof consists of carefully placed slabs creating a passage roughly 0.8 metres wide and 0.9 metres high. At its northern terminus, collapsed stone blocks any further exploration.

This archaeological site at An Leargain Bhreac represents a type of fortified homestead common throughout Ireland during the early medieval period. Cashels like this one served as protected farmsteads for prosperous families, whilst souterrains provided secure storage for food and valuables, and potentially served as hiding places during raids. The combination of defensive walls and underground passages reflects the uncertain times in which they were built, when communities needed to balance daily agricultural life with the ever-present need for security.