That label understates matters considerably. What lies beneath the surface here is a souterrain, an artificially constructed underground passage or chamber, typically built during the early medieval period and associated with nearby settlement. The cartographers of a century ago may not have been entirely wrong, though; from ground level, the site presents itself as little more than a pair of depressions in the earth, one roughly two metres across and another, shallower hollow about four metres wide sitting six metres to the south-east. Peer into the first, and collapsed stone lintels are visible in the gloom below.

The souterrain sits within a rath, the circular earthen enclosure that formed the basis of many early Irish farmsteads, defined by a bank and ditch and serving both as a boundary marker and a measure of the occupant's status. Souterrains were commonly built within or close to raths, most likely for cold storage of foodstuffs and possibly as a place of refuge. At Carrowhubbuck, the main depression, located a short distance west of the rath's centre, is where the roof has given way, exposing those fallen lintels. The second, broader hollow to the south-east has not been excavated or fully assessed, but its proximity and character suggest it belongs to the same underground structure, perhaps a second chamber or a connecting passage that has similarly subsided over the centuries.