The Ordnance Survey's first-edition six-inch map recorded it with a hachured outline, the standard cartographic shorthand for an earthwork or enclosure, but placed it slightly to the east of where it actually sits. That small navigational error is, in its own way, fitting for a site whose nature has also resisted easy classification.

When the site was inspected in 1998, what emerged was a subcircular enclosure roughly 38 metres across at its widest point, defined by drystone slab walling. Drystone construction uses no mortar, relying instead on the careful arrangement of stones to hold their own weight, and this walling, standing between 0.8 and 1.2 metres high and up to 0.6 metres thick, appeared to be of relatively modern origin rather than early medieval. A cashel, by contrast, is a stone-walled enclosure typically associated with the early medieval period in Ireland, and this part of Clare is thick with them. The enclosure at Crumlin sits within an extensive field system surrounded by associated cashels and enclosures, which makes the apparently modern character of its walling all the more curious. Some upright stones on the eastern side suggest a probable entrance. More puzzling still is a pronounced hollow in the eastern half of the interior, measuring 29 metres long, 9 metres wide, and dropping to a depth of 1.4 metres. Its origin and purpose are not recorded, and it is that unexplained depression, as much as anything else, that gives the site a quietly unsettled quality.