Look more closely at the one at Coolrus, however, and you will find a carefully carved hollow in its flat upper surface, a U-shaped oval depression cut deliberately into the rock, its purpose now uncertain but its human origin clear enough. This is a bullaun stone, a type of carved boulder found widely across Ireland, typically associated with early Christian or pre-Christian activity. The hollows, known as bullauns, are thought to have served various functions over the centuries, from mortars for grinding to vessels holding water believed to have curative or ritual properties.

The stone at Coolrus came to light in 1999, not through any dedicated archaeological survey but as a consequence of paperwork. It was identified during the compilation of an Environmental Impact Statement prepared in advance of a proposed quarry development in the area, and subsequently recorded by Gregory in 2000. The boulder itself is a substantial piece of granite, measuring 2.3 metres by 1.4 metres and standing 0.85 metres high, with a flat upper surface into which the principal hollow has been cut. That hollow has a depth of 0.21 metres and an opening measuring 0.48 metres by 0.4 metres, making it a well-defined and deliberate feature. There are three other possible depressions elsewhere on the stone, though all are shallow and indistinct enough that their status as intentional workings remains uncertain. The record was compiled by Denis Power and uploaded to the national database in August 2011.

The site lies adjacent to a field boundary, which gives some sense of how embedded in the ordinary agricultural landscape these ancient features can become. Access will depend on local field conditions and land ownership, so some enquiry beforehand is sensible. The stone itself rewards patient looking; the main hollow is unmistakable once you are positioned above it, but the shallower possible depressions require good raking light to read at all, making an overcast day or late afternoon visit more useful than bright midday sun.