Roughly 70 metres in diameter and defined by four concentric ramparts, it exists, for all practical purposes, only from the air. At ground level, centuries of agriculture have smoothed away every visible trace, leaving the site entirely invisible to anyone standing on it.

What makes Knockeen particularly interesting is its complexity. A single-rampart enclosure, often called a ringfort, was the standard form of enclosed settlement across early medieval Ireland, typically used by farming families as a combination of homestead and livestock enclosure. Four ramparts is unusual, and the fact that three of the outer banks sit in close proximity to one another suggests something more deliberate, possibly a site of higher status or one that accumulated defensive works over time. The enclosure sits on a gentle north-east facing slope, a detail that aerial photography has preserved with some precision. The site came to wider notice through cropmark evidence captured in aerial photographs, a technique in which buried ditches and banks, invisible at the surface, reveal themselves as variations in crop growth during dry summers, the vegetation above a buried feature ripening or wilting at a slightly different rate to the surrounding ground.