Quartz had a particular significance in prehistoric Ireland, appearing repeatedly at ceremonial sites, and here the two flanking stones feel less like a practical threshold and more like a deliberate announcement. Beyond them, twenty-nine substantial boulders form a ring thirty metres across, originally set contiguous, meaning each stone touching or nearly touching the next, a continuous wall of granite rather than the spaced uprights seen at many other Irish circles. Some stones still stand upright; others were set deliberately on their long axis, lying flat but placed with intent. Several carry wedge marks and boreholes, the traces of later attempts to break them up, which tells its own quiet story about attitudes to the monument in more recent centuries.

The circle sits on a natural rise in County Wicklow, with the River Slaney running roughly 250 metres to the south. What makes Castleruddery particularly unusual among Irish stone circles is its elaborate layering of enclosures. Around the stone ring itself runs an earthen bank, a broad embankment forty metres in diameter, up to four and a half metres wide and a metre high, whose terminals curve around to frame the quartz entrance stones. Beyond that, aerial photography has revealed cropmarks, the ghostly outlines of buried ditches visible in dry summers from the air, showing two further enclosures concentric with the bank: a narrower fosse at roughly fifty metres diameter and a larger one at around eighty metres. The single upright stone standing some fifteen metres east of the entrance, out beyond the bank, adds another element whose function is not fully understood. Scholars including Aubrey Burl, who catalogued stone circles across Britain and Ireland, noted the site in the 1990s, and earlier references appear in the work of Walshe in 1931 and Leask in 1945, suggesting a long thread of antiquarian and archaeological attention.

The northern arc of the circle is the best preserved; the southern side has suffered more, and a later field bank cuts across the outer earthwork at the south. The interior of the circle itself is otherwise clear of features, which leaves the space feeling open and uncluttered once you are standing within it.