The discovery revealed a souterrain, a type of stone-built underground passage constructed in early medieval Ireland, typically for storage or refuge, that had lain sealed and forgotten beneath the farmland at Doonore.

The passage ran north to south and was roofed with flat stone slabs, known as flags, a standard construction technique for souterrains across Ireland. No date was recorded for the find, but local information cited in 1946 places the discovery sometime before that year, meaning the structure had already been disturbed for decades before any formal note was made of it. Nothing of the passage is visible above ground today, and there is no surface feature to mark where it once lay.