It has been there for a very long time, and for most of that time nobody outside the immediate locality knew it existed. What makes it stranger still is that the carvings on it almost certainly predate the structure around it by centuries, which means the stone was already ancient when whoever built the souterrain decided to incorporate it into their wall.

The site is the ringfort known as Rathduff, in the townland of the same name near Emper in County Westmeath. A ringfort is a roughly circular enclosure, typically defined by an earthen bank and ditch, used as a farmstead during the early medieval period. Beneath this one runs a souterrain, an underground dry-stone passage or chamber used for storage or refuge, entered from the north side of the ringfort interior. The souterrain opens into a well-constructed central chamber with two passages leading off it. It was first brought to wider attention by Hugh Weir in 1938. In the right-hand passage, built into the wall, is the carved stone, with a visible face measuring approximately 85 by 28 centimetres. The decoration, described in detail by O'Reilly in 2010, includes irregular linear grooves, a single cup-mark, four cup-and-ring motifs, and a concentric circle motif around 14 centimetres across. Cup-and-ring marks are among the most common forms of prehistoric rock art in Ireland and Britain, consisting of a small circular depression carved into stone and surrounded by one or more incised rings. What sets the Rathduff stone apart is a detail within its concentric circle motif: rather than enclosing the usual cup-mark at its centre, the rings surround a raised circular area roughly 5 centimetres in diameter. There is also a radial groove cutting through the lower portion of the circles, and a long meandering linear groove, described as a tail, that runs from the outer ring down to the lower right edge of the stone. A Bronze Age flat cemetery has been identified in an adjoining field to the south-east, suggesting the wider landscape around Rathduff was in use for ritual or burial purposes long before the ringfort was built.

The site sits on private farmland and is not accessible to the public.