This is a fulacht fia, a type of prehistoric cooking site typically consisting of a horseshoe or kidney-shaped mound of heat-shattered stone built up around a trough. The usual interpretation is that stones were heated in a fire, dropped into a water-filled pit to bring it to the boil, and used to cook meat, though some researchers have proposed additional uses including textile processing or bathing. The Ballyganner example follows the classic form closely: a kidney-shaped mound open to the north-west, partially enclosing a fairly level central area roughly six metres by three metres.

The mound itself measures approximately 14.5 metres on its longer axis and 11.5 metres across, and the two arms are noticeably unequal. The north-eastern arm is lower, rising only about 0.4 metres on its outer face, while the south-western arm stands a little taller at around 0.7 metres externally. The site sits within a large multiperiod field system, meaning the landscape around it has been divided, worked, and reworked across many centuries by different communities. A later drystone field wall, the kind built without mortar by stacking flat stones, cuts directly across the north-eastern arm, a small physical reminder that later farmers had little reason to treat the mound as anything other than convenient ground. About seven metres to the south-west lies a separate cairn, a pile of stones that may represent a burial or clearance feature from another phase of activity entirely, giving the hilltop a quietly layered quality that its open, windswept appearance does little to advertise.