In the townland of Cullenagh Beg in County Galway, within the interior of a rath, a shallow trench in the earth is all that now marks what the Ordnance Survey cartographers of 1838 simply called a cave. A rath, for those unfamiliar with the term, is a roughly circular earthen enclosure, typically dating from the early medieval period, built as a farmstead and bounded by one or more banks and ditches. That a cave should have existed within one is not impossible; such enclosures are sometimes associated with souterrains, underground stone-lined passages used for storage or refuge. Whether this was something of that kind, or something older or more unusual, is no longer easy to say.

The depression that survives today sits in the north-western quadrant of the rath's interior. It runs roughly north-north-west to south-south-east, measures about twelve metres in length and two metres across, and reads in the landscape as a long, narrow sinking of the ground. McCaffrey, writing in 1952, recorded it and connected it to the feature marked on the first edition six-inch Ordnance Survey map, which was surveyed in 1838. That map notation suggests the cave was still a recognisable presence in the mid-nineteenth century, or at least that local knowledge of it was strong enough to warrant inclusion. By the time of the twentieth-century record, only the depression remained, and the cave itself, whatever its true form, had effectively vanished.