What survives is barely enough to read as a deliberate human construction, and yet the outline persists.

The site is a subcircular rath, the most common form of early medieval enclosure in Ireland, typically built as a defended farmstead between roughly the fifth and twelfth centuries. They were usually defined by one or more earthen banks and ditches enclosing a domestic space where a family would have lived and kept livestock. At Castlegar, that enclosure measured approximately thirty metres north to south and twenty-seven metres east to west, modest even by the standards of single-ring examples. Today only a bank survives at the western side; elsewhere the perimeter has been reduced to a scarp, a low change in ground level that suggests where the original bank once ran. Quarrying has eaten into the monument at the south-east and west, which accounts for much of what is missing. A series of additional banks lies to the east of the main enclosure; these may belong to a later phase of activity at the site, though their precise date and function remain uncertain.