What remains visible is a drystone-built rectangular chamber running roughly south-west to north-east, measuring around six metres in length, with a further six metres of fallen material suggesting the original structure once extended considerably further in the same direction. A modern breach at the south-western end now serves as the only way in, an opening made not by its original builders but by someone in much more recent times.

The chamber sits in the south-western quadrant of a large enclosure, a relationship that is almost certainly not coincidental. Souterrains, which are man-made underground passages or chambers built from stone without mortar, are typically associated with Early Medieval settlement sites in Ireland, dating roughly from the seventh to the twelfth century. They are found tucked within or alongside ringforts and enclosures across the country, and their precise function has long been debated; current thinking favours a combination of uses including cool storage for perishables and refuge during times of threat. The Cashla example follows this pattern, positioned within a wider enclosed site and constructed using the drystone technique common to the type, where stones are carefully fitted together without any binding material.