The entrance is just 0.8 metres wide and 0.5 metres high, barely enough to squeeze through, which is entirely typical of a souterrain, an underground stone-lined passage or chamber built during the early medieval period, generally thought to have served as a place of refuge, cool storage, or concealment.

The passage runs eastward from the entrance, stone-built and roofed with flat stone lintels, sloping gently downward for around five metres before the construction method changes. At that point, rather than being built up from dressed stone, the tunnel becomes rock-cut, hewn directly from the bedrock, varying in width as the natural material allowed. Local knowledge holds that the passage continues from there, turning south and then east again, though how far it extends has not been formally recorded. The surface to the south-east of the entrance shows a series of depressions where sections of the roof have collapsed over time, which gives some impression of the route the structure takes underground, even where the passage itself is no longer safely accessible.