A lime kiln is essentially a large furnace used to burn limestone at high temperatures, converting it to quicklime for use in mortar, plaster, and agricultural soil improvement. What made the Mondaniel example unusual was not its function but its archaeology: beneath the soil lay two kilns, one nested inside the other, each representing a distinct phase of construction and use.

The earlier structure, Phase I, was sunk into a pit roughly 7.5 metres in diameter and about 4 metres deep, dug directly into the natural subsoil. Its walls, built from randomly coursed sandstone blocks that had been vitrified, or fused, by prolonged exposure to intense heat, were battered outward from the base, giving the structure a slightly splayed profile. A wedge-shaped entrance and raking-out area to the west allowed workers to stoke the fire and remove spent material. At some later point, a second, smaller kiln was constructed inside the first: a new inner wall was built, the floor level was raised to align with the stoking pit, and the gap between the old and new walls was packed with rubble. Both phases were identified as flare kilns, a type in which fuel and limestone are loaded together and burned in a single firing, on the basis of internal ledges and unburnt limestone blocks found during excavation. The excavator noted that the Phase II rebuild would have made the process more efficient and simplified the removal of the finished lime. A second kiln was found just three metres to the east, though whether the two were in use at the same time or in sequence could not be established. Radiocarbon dating produced frustratingly wide ranges, from 1520 to 1950 for the earlier phase and 1640 to 1950 for the later one, and no artefacts were recovered to narrow things down. By 1842, when the Ordnance Survey mapped the area at six inches to the mile, the kilns had already gone out of use and a field boundary had been built directly over them.