At Bohernabreena, in the Dublin Mountains, a ringfort once occupied a stretch of steeply sloping grassland, its oval outline recorded and measured, its interior levelled, and now, at ground level, entirely invisible. The site persists mainly as a cartographic memory.

Ringforts, sometimes called raths, are the most common archaeological monument type in Ireland. They are typically circular or oval enclosures defined by an earthen bank and ditch, built during the early medieval period roughly between the fifth and twelfth centuries, and used as enclosed farmsteads by families of varying social rank. This particular example was documented by Healy in 1975, who described it as having a level interior with a length of roughly 30 metres and a width of 20 metres, dimensions that suggest a modest but not unusual enclosure for the type. Earlier still, the 1937 Ordnance Survey six-inch map showed it as a hachured oval enclosure set in rough pasture, the hachuring being the mapmakers' way of indicating an earthwork through shading rather than contour. The site sits on ground that falls away steeply to the west, which would have made the levelled interior a deliberate piece of construction rather than a natural convenience.

Bohernabreena is best known today for its reservoirs and the Glenasmole valley, and the ringfort lies within that broader upland landscape south of the city. Because there are no visible remains at ground level, there is little to see on a visit in the conventional sense. The value here is more in the act of orientation, of standing on a hillside and knowing that the ground beneath was once shaped by hands that needed the land to be flat and enclosed. The 1937 OS map is the most useful companion for locating the approximate position. Given the steeply sloping terrain and rough pasture, sturdy footwear is advisable, and the site will read more clearly in low winter light or after rain has defined the subtle undulations that survive, if any do.