Most souterrains, the underground passages and chambers built in stone during the early medieval period and associated with ringforts and cashels, follow a roughly linear or gently curving plan. This one branches. Seen from above, it forms a clear Y, a configuration that is far from standard and raises quiet questions about how it was used and by whom.

The structure sits within a cashel, a type of stone-walled enclosure common in the west of Ireland, typically built to protect a farmstead and its inhabitants during the early medieval period. The souterrain's main axis runs roughly north-northeast to south-southwest and measures 13.8 metres in length. A shorter arm, 9.3 metres long and 1.6 metres wide, branches off near the southern end of the western wall and runs in a slightly different direction, creating the fork that defines the whole plan. Drystone walling, that is, stonework laid without mortar, remains visible along the side-walls, a reminder of the care that went into lining a passage intended to be concealed. The souterrain is now largely roofless, though two lintels survive at the northwest and northeast ends, giving some sense of how the original covering was constructed. The interior is rubble-filled, which limits what can be seen directly, but the overall geometry of the underground plan has been recorded.