In 1904, the roof of a stone-built souterrain collapsed in the western half of a rath at Ardraw, briefly exposing what lay beneath: two narrow passages, carefully constructed and then, for centuries, entirely invisible. A souterrain is an underground stone-lined tunnel or chamber, typically associated with early medieval ringforts, and thought to have served as storage space, refuge, or both. This one had managed to stay hidden long after the rath above it had ceased to be anyone's home.

When the collapse revealed the passages, the larger of the two ran northeast to southwest, measuring around 3.55 metres in length and narrowing dramatically from roughly 1.75 metres wide at one end to just 0.6 metres at the other. Its lintelled roof, formed from flat stones laid across the top, sat nearly 1.6 metres below the interior surface of the rath. A second, smaller passage nearby ran roughly north to south and measured about 1.2 metres in each direction. By the time the Cork and Kerry Field Club recorded the site in 1940, the passages were already in a sorry state, the stones that had formed them thrown about and the structure torn up and damaged. Among the scattered stonework was what the Field Club described as a horseshoe-shaped stone from a crawl doorway, most likely a porthole slab or arch stone of the kind used to create low, restrictive internal openings that could be easily defended or blocked. Similar stones have been identified in souterrains at Kimego West and Kealduff Upper, also in Kerry, suggesting a shared constructional tradition across the Iveragh peninsula. Today, no trace of the souterrain is visible at the surface.