The structure he chose for the purpose, known locally as An Chathair Gheal, the bright or white caher, had walls nearly five and a half metres thick at the base, two internal terraces linked by opposing flights of steps, and an entrance passage flanked by portal-like slabs that are still standing. The lamb shelter is gone. The caher is not.

A caher, or cathair, is a stone ringfort, a type of enclosed settlement built throughout early medieval Ireland, typically by farming families of some social standing. Cahergal is the most southerly of a cluster of three such enclosures on the northern side of the Valentia river estuary in south Kerry, set on the crest of a low ridge with a natural rock-face along its northern edge. Its circular rampart encloses an area roughly 26 metres across and survives to an external height of four metres at the south-west. That wall is no rubble heap; it consists of a carefully laid drystone facing over a rubble core, with a deliberate inward slope, or batter, on both faces that gives it structural stability. By the time the Office of Public Works began conservation work in the 1980s and 1990s, the rampart had been breached to the north-north-east and much of the southern and western exterior had collapsed; early photographs from the Lawrence Collection documented the extent of the deterioration. Excavation of the central hut, carried out by Manning in 1991 and 1992, found an occupation layer over the floor, a large central hearth-pit, several hundred stake-holes, and fragments of quern-stones, sheet bronze, iron slag, and tuyère fragments, the last being pieces of the clay nozzles used to direct air into a forge. The hut itself had three entrances, one of them later blocked, and local tradition recorded by Chatterton in 1839 held that its roof had originally been corbelled, a technique in which courses of stone are progressively cantilevered inward until they meet at the top.

A small rectangular structure that once stood against the inner face of the rampart to the north attracted some scholarly interest before it was dismantled by the OPW in the early 1980s. Lecky, writing in 1914, suggested it might be an oratory, though it did not appear on Dunraven's earlier plan of the site from 1875, and Françoise Henry concluded in 1957 that it was of modern date. A large flat slab still lying inside the caher bears two sizable circular depressions on its upper surface, whose purpose has not been established.