Above it, the earthen bank of a ringfort, a univallate rath, rises little more than a gentle swell from the inside but stands 1.75 metres high on its outer face. A fosse, the shallow ditch encircling the bank, is barely perceptible across most of its circuit. No entrance to the enclosure has been identified. The land to the north slopes away gradually towards Tralee Bay, and on a clear day the views open out in every direction, which makes the site's quiet self-concealment all the more striking.

The Kerry Field Club recorded a circular stone hut inside the enclosure as far back as 1945. That structure has since collapsed to a spread of loose stones lying slightly north of centre, but the souterrain it once sheltered has survived in considerably better shape. A souterrain is an underground passage and chamber built of drystone masonry, associated with early medieval settlement in Ireland, and typically used for storage or refuge. The one at Duagh runs for approximately 9.2 metres in total. Its first section heads north-west for 3.7 metres, roofed by eight flat slabs and narrow enough at its far end, just 0.45 metres wide, that movement through it would have demanded care. The passage then angles and continues north-north-west for a further 5.5 metres before meeting a rectangular chamber measuring 4.9 metres long, 1.3 metres wide, and 1.8 metres high, its side walls inclining slightly inward to reduce the span at roof level. The original connection between passage and chamber was a creepway closed by a porthole slab, an opening of only 36 by 38 centimetres, now blocked, though the slab itself remains in place. At some point in relatively recent times the end wall of the passage was broken away to provide easier access to the chamber, bypassing the original entry entirely. J. Cuppage described the site in detail in the 1986 Dingle Peninsula archaeological survey.