In the early twentieth century, a surface opening gave access to a drystone-built structure below. Drystone construction here means what it says: stone laid without mortar, shaped and stacked to hold its own weight, a technique used across early medieval Ireland for everything from field walls to underground refuges. At some point after that early access, the opening was deliberately infilled, and the chamber disappeared back into the earth.

The underground structure sits within a rath, a type of enclosed settlement typical of early medieval Ireland, usually defined by one or more earthen banks and ditches. Souterrains, the underground chambers or passages sometimes found within them, were likely used for storage, shelter, or concealment, though their precise function is still debated. When the rath at Park was inspected in 1996, the souterrain itself remained hidden, but a large stone slab was observed protruding from the ground in the north-western quadrant of the interior. This slab may be a displaced lintel, the kind of flat capstone that would originally have formed part of the roof of a drystone passage. The ground level in that area is very slightly raised, a subtle unevenness that, once you know what to look for, suggests something lying just below the surface.