The name places it within one of the most widely distributed story cycles in Irish folklore, the elopement of Diarmuid and Gráinne, in which the pair flee across Ireland from the pursuing Fionn Mac Cumhaill. Countless hollows, caves, and earthworks around the country were assigned this same romantic label by local tradition, making the name itself a kind of geographical folklore, a repeated folk explanation applied wherever a natural or man-made depression invited the imagination.

What is genuinely interesting here is the gap between the name and the thing. On the earlier Ordnance Survey maps of 1841 to 1842, the site appears to be a circular enclosure, the kind of feature that elsewhere might indicate a ringfort or a small defended settlement. By the later edition of 1914 to 1915, it seems to have been reinterpreted as a simple depression. A nineteenth-century observer recorded in the Ordnance Survey Name Books that it was 'a small fort at the brink of the River Shannon', and was at pains to clarify that it was 'not a Cromlech but a mere hollow in the cliff so called'. A cromlech being a megalithic tomb formed by large upright stones capped with a horizontal slab, the note suggests locals or visitors may have been reading more ancient purpose into the site than the evidence warranted. The same source identifies Diarmuid, rendered here as 'Deermud', as 'one of the Irish Champions called Feenthin', a reference to the Fianna, the legendary warrior band of Fionn Mac Cumhaill's cycle. The slippage between an earthwork, a hollow, and a mythological sleeping place tells you something about how landscape features acquire stories and then shed their physical clarity over time.