The main enclosure, known as a rath, is an oval raised earthwork measuring roughly 29 metres on its longer northeast-southwest axis and just under 20 metres across. A rath is a type of ringfort, typically a circular or oval area enclosed by one or more earthen banks, used as a farmstead or high-status residence during the early medieval period in Ireland, broadly between the fifth and twelfth centuries. Here, the southwestern side retains a recognisable bank, while elsewhere the boundary survives as a scarp, a natural-looking slope that is in fact the eroded edge of the original earthwork, rising in places to around 4.5 metres in height. The D-shaped annexe adjoining it to the northeast consists of a low platform defined by its own scarp and measures approximately 15 metres along its main axis. Annexes of this kind are relatively uncommon and may have served as enclosures for livestock, workshops, or other activities kept separate from the main domestic space. Within the interior of this annexe there is a quarry pit and what appears to be a souterrain, an underground stone-lined passage or chamber, typically used in early medieval Ireland for storage or as a place of refuge. The souterrain at Derrymore has not been excavated, so its extent and condition remain unconfirmed.