The whole structure fits within dimensions that feel almost domestic in their smallness, yet it represents a type of construction that took considerable effort and knowledge to build.

A souterrain is an underground structure, typically earth-cut or stone-lined, associated with early medieval raths, the circular earthen enclosures that once served as farmsteads across Ireland. Their precise function is still debated; storage, refuge, and drainage have all been proposed. The Laharan example sits off-centre to the north within a rath, and came to light in 1999 through local, non-archaeological investigation rather than any planned excavation. When the rubble blocking a narrow shaft, roughly 72 centimetres east to west and 43 centimetres north to south, was cleared away, it opened into a dome-shaped earth-cut passage running approximately two metres in length and just 63 centimetres high. At the southern end of that passage, a creepway barely 61 centimetres wide leads into a small subrectangular chamber measuring around 1.8 metres long. The chamber is roofed by four lintels, the southernmost being a substantial square slab of roughly one metre by one metre, with three narrower rectangular slabs beside it. At the time of inspection the passage had become waterlogged, and the chamber itself was filled with earth to within 30 to 40 centimetres of its roof, meaning whatever the floor might once have revealed remains, for now, out of reach.