Cahersiveen, known in Irish as Cathair Saidhbhín, derives its name from this ancient cashel, a type of stone-walled ringfort once common across Munster and the west of Ireland. The town has long since grown around and over it, and what was once a defined enclosure on a slight rise above the south bank of the Valencia river is now little more than a low, stony bank curving through an urban landscape. When the first edition of the Ordnance Survey map was produced, the site was marked simply as 'Caves', a label that suggests local memory of its underground features rather than any clear understanding of what the structure once was.

Local tradition holds that the stone from the cashel's enclosing rampart was carted away for use in the construction of the nearby RIC barracks and the railway bridge, a fate that was common enough for ancient stonework in the nineteenth century, when building materials were scarce and the past was not yet a protected resource. What survives today is a subcircular area measuring roughly 21 metres north to south and 28 metres east to west, with a bank averaging 0.8 metres high on the outside and 0.5 metres on the inside, about 4.5 metres wide. The southern arc is barely distinguishable, partly because a modern road now skirts it. Beneath the surface, there are reputed to be two souterrains, which are narrow stone-lined underground passages typically associated with early medieval ringforts and used variously for storage or refuge. One of these extends beyond the enclosure boundary to the southeast. As for the Sadbh element in the town's Irish name, its origins remain uncertain, noted as unclear by T. J. Westropp as far back as 1912.