Yet that is what survives at Killogrone on the Iveragh Peninsula in County Kerry: the probable remains of a horizontal-wheeled water mill, a type of small-scale milling technology that was widespread in early medieval Ireland and remained in use in the west of the country for centuries. Unlike the more familiar vertical waterwheel, the horizontal mill, sometimes called a tide mill or click mill, placed its wheel flat in a channel of fast-moving water, directly driving the millstone above without the need for gearing. The mechanism was simple, local, and effective.

The structure at Killogrone was interpreted by A. T. Lucas, writing in 1953, as the wheel-house of just such a mill. The two parallel drystone walls, averaging 3.5 metres long and surviving to an internal height of 2.6 metres, are built from regular flat slabs with a slight outward bow at their centres, which Lucas argued would have created enough clearance for the wheel to rotate. A large flat slab, measuring 2.25 metres by 1.55 metres and just 12 centimetres thick, found outside the structure, he believed originally lay across the top of the walls as the floor of the mill-house proper; it carries a central perforation of 9 centimetres in diameter, through which the shaft connecting wheel to millstone would have passed, and a second smaller hole towards its western edge. A notched upright slab leaning against the southern ends of the walls was interpreted as the support for the fore end of the flume, the wooden channel that directed water onto the wheel. About 12 metres of diverging stony banks extending southward from the structure were read as the remains of a headrace, the earthwork channel that fed water to the mill. Not everyone has found Lucas's reconstruction convincing: Colin Rynne, writing in 1988, argued that the wheel-house as described would have been too narrow to accommodate a functioning wheel. The question has not been resolved, and the site itself offers no easy answers, being heavily overgrown and obscured by internal collapse.