At Rathbaun in County Galway, the Ordnance Survey marked a feature simply as "Cave" on both its 1838 edition and again on the 1921 revision of the six-inch map, suggesting that whatever lay there was considered significant enough to record across nearly a century of cartography. Today, no visible trace of it remains.

The cave in question is believed to be a souterrain, an underground stone-lined passage or chamber typically constructed during the early medieval period, often beneath or beside a rath. A rath, also called a ringfort, is a circular enclosure defined by an earthen bank and ditch, used as a farmstead and place of security. Souterrains were commonly built within them, serving variously as storage spaces, refuges, or escape routes. This one sits inside just such a rath at Rathbaun. When the archaeologist McCaffrey visited the site in 1952, he was unable to locate the souterrain at all, noting that dense overgrowth had obscured whatever opening or depression might once have guided a visitor to it. A re-inspection carried out in November 1982 found the same: no surface trace, no discernible entrance, nothing to indicate that anything lay beneath the ground.