The monument they form is a cursus, a type of long, linear Neolithic enclosure whose precise purpose remains one of prehistory's more persistent puzzles. Cursus monuments, named somewhat fancifully after Roman racetracks by early antiquarians, are generally thought to have been ceremonial or processional in character, though exactly what that means in practice is still debated. What makes the one at Ballyoskill quietly unusual is its topography: rather than sitting on flat or gently undulating ground as many cursus monuments do, this example runs steeply downhill, widening as it descends, and terminates not at its lowest point but at the crest of the hill with a curving bank.

First identified as a possible monument in 1955, the structure presents some intriguing details on close examination. The interior of the cursus sits lower than the ground outside the banks, which themselves appear to contain a high concentration of local shale, suggesting there may be stone walling beneath the grass sod rather than purely earthen construction. At the upper, eastern end, the two banks are only 7.7 metres apart, but the monument fans out considerably as it runs westward, reaching 20 metres between banks just above the first field boundary. Below that point, the banks become harder to trace and may have been absorbed into existing field boundaries over the centuries. The orientation shifts too, moving from due west at the top for around 125 metres, then swinging to west-south-west for roughly another 100 metres. From the crest of the hill, the views open up dramatically to the south, west, and north, with a particularly clear line of sight to the north-east, though that last view is only available from the very top of the monument itself.