This subcircular earthwork measures approximately 42 metres across from northeast to southwest and 40 metres from northwest to southeast. The monument’s defining feature is its massive earthen bank, which rises to 1.3 metres on the interior side whilst presenting a more formidable face to the outside world at between 3.5 and 4 metres in height. Trees now grow along this ancient defensive bank, lending the site a particularly atmospheric quality.

The fort’s original design remains somewhat mysterious, with archaeological surveys revealing tantalising but inconclusive features. To the southeast, faint traces of what may have been a defensive ditch can still be detected, whilst 7.5 metres to the southwest, a smaller earthen bank curves to follow the enclosure’s outline before continuing as a modern field boundary. Whether these elements formed part of the original Iron Age construction or represent later additions remains unclear. The eastern entrance has unfortunately been landscaped in more recent times, obscuring its original form.

Within the fort’s level interior, one intriguing feature catches the eye: an oval underground chamber measuring 1.7 by 1 metre, constructed from dry stone and roofed with stone slabs. Located in the southeastern sector, this structure is believed to have served as a well, providing water to the fort’s inhabitants. Such ringforts typically date from the early medieval period, roughly between 500 and 1200 CE, when they served as defended homesteads for farming families of some local importance. Rathdonnell Fort stands as a tangible link to this era when such fortified farmsteads dotted the Irish landscape, centres of agricultural life and local power in a turbulent age.