Sitting on the northern bank of the Cashen River in north County Kerry, it has been so thoroughly altered by drainage works that the original form can only be guessed at. The inner raised area, roughly semicircular and standing about two metres high, survives, but a later earthen overflow bank cuts across it from the south, and a channel now wraps around the site from west to north and east. Reading the landscape here requires a certain tolerance for ambiguity.

A ringfort, or rath, was a roughly circular enclosure typically defined by one or more earthen banks and ditches, used as a farmstead or defended homestead during the early medieval period in Ireland. The fosse, the ditch that would normally have ringed this one, may well still be present in altered form. According to the North Kerry Archaeological Survey, compiled by C. Toal and published in 1995, the encircling channel was possibly an original fosse that the Board of Works deepened and widened when they cut a drainage channel through the site, probably sometime in the 1960s. That intervention, intended to make the low-lying ground beside the Cashen more workable as farmland, left what the survey describes plainly as a very distorted picture. The fort takes its name from the townland of Rahoonagh, and its internal diameter runs to 28.7 metres east to west, which places it within the typical range for a site of this type, even if little else about it is now typical.