A feature marked as 'Druid's Altar in ruins' appeared on a pre-publication field map created for the Ordnance Survey, yet when the official OS 6-inch map was published between 1845 and 1848, this tantalising detail had vanished without explanation. No documentation exists in the Ordnance Survey archives to explain why it was removed, leaving historians to wonder what the original surveyors encountered that day in the field.

The site itself offers no clues to modern visitors; whatever remains might have existed in the mid-19th century have long since disappeared. The original surveyors' decision to label it a 'Druid's Altar' suggests they saw something they believed to be ancient and ritualistic, though this terminology reflects Victorian romanticism about Ireland's prehistoric past rather than any actual Druidic connection. During this period, it was common practice to attribute mysterious stone structures to the Druids, regardless of their true origin or purpose.

Today, the site is classified simply as an unclassified megalithic tomb, a designation that acknowledges both its potential archaeological significance and the frustrating lack of concrete evidence about its nature. The Survey of the Megalithic Tombs of Ireland, compiled by Eamon Cody in 2002, includes this phantom monument in its comprehensive catalogue, ensuring that even vanished sites remain part of the archaeological record. Whether it was a passage tomb, a stone circle, or something else entirely, the Knockfair site reminds us that Ireland's ancient landscape holds stories that sometimes slip through the fingers of history.