A souterrain, the term used for the dry-stone or earth-cut underground passages built in early medieval Ireland, typically associated with nearby settlement sites, this particular example is recorded as an isolated find, with no obvious surface features to announce it. What makes it quietly interesting is how much considered construction went into something so thoroughly out of sight.

The structure was first described by Gillman in 1896 and later examined by McCarthy in 1977. It consists of a stone-built entrance passage and two earth-cut oval chambers. The passage, oriented roughly north to south, measures just over two metres in length and less than a metre wide, roofed with four stone lintels and reached from the surface by three stone steps at its southern end. From the eastern side of the passage, a low creepway, the kind of tight connecting gap that required a person to crouch or crawl, leads into the first chamber, which measures roughly two and three-quarter metres long and just over a metre high. A second creepway connects that chamber to a slightly larger second one beyond it, the two lying parallel to each other and at right angles to the passage. The overall layout is compact and deliberate, with the chambers positioned side by side rather than in a simple linear sequence.

The function of souterrains remains a matter of discussion among archaeologists. Cold storage, refuge, or a combination of both are the most commonly proposed explanations. Whatever its original purpose, the Deelish example is notable for the precision of its recorded dimensions and the relative completeness of its surviving form, at least as documented. The creepway connections between sections would have made movement through the structure slow and awkward, which may have been entirely the point.